Having replaced an older version of Linux Mint with Mate 19.3 I can no longer detect Wi-Fi. I do have Ethernet connection but it frustrates me that the Wi-Fi option is no longer available?
Have tried clicking on NVIDIA-340 driver, that caused machine to crash and had to reload system again. So have stayed with the xserver as it works well.
Have also tried installing WiFi Radar detect but when it searches the reply is [wlp7s0 Interface doesn't support scanning : Network is down]

This error message indicates that the installation disk is still in the /etc/apt/sources.list file, where software repositories are listed. As root, you can edit that file with a simple text editor to remove or remark out the reference to the disk. [sudo [editor name] /etc/apt/sources.list)

While you are troubleshooting this, it would be wise the establish a wired connection so you have network connectivity during the troubleshooting process.

The key information is which wireless chipset is installed in this machine. You can find that out by running the command lspci in a terminal. Run the command, then post the relevant output here, being sure to surround it with "code" tags which become available when you click the "Go Advanced" button beneath the compose/edit post window.

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New to this so do not understand all your advise like Ǵo Advanced, but here is the output:
mike@mike-Compaq-Presario-CQ60-Notebook-PC:~$ lspci
00:00.0 RAM memory: NVIDIA Corporation MCP78S [GeForce 8200] Memory Controller (rev a2)
00:01.0 ISA bridge: NVIDIA Corporation Device 075e (rev a2)
00:01.1 SMBus: NVIDIA Corporation MCP78S [GeForce 8200] SMBus (rev a1)
00:01.3 Co-processor: NVIDIA Corporation MCP78S [GeForce 8200] Co-Processor (rev a2)
00:01.4 RAM memory: NVIDIA Corporation MCP78S [GeForce 8200] Memory Controller (rev a1)
00:02.0 USB controller: NVIDIA Corporation MCP78S [GeForce 8200] OHCI USB 1.1 Controller (rev a1)
00:02.1 USB controller: NVIDIA Corporation MCP78S [GeForce 8200] EHCI USB 2.0 Controller (rev a1)
00:04.0 USB controller: NVIDIA Corporation MCP78S [GeForce 8200] OHCI USB 1.1 Controller (rev a1)
00:04.1 USB controller: NVIDIA Corporation MCP78S [GeForce 8200] EHCI USB 2.0 Controller (rev a1)
00:06.0 IDE interface: NVIDIA Corporation MCP78S [GeForce 8200] IDE (rev a1)
00:07.0 Audio device: NVIDIA Corporation MCP72XE/MCP72P/MCP78U/MCP78S High Definition Audio (rev a1)
00:08.0 PCI bridge: NVIDIA Corporation MCP78S [GeForce 8200] PCI Bridge (rev a1)
00:09.0 IDE interface: NVIDIA Corporation MCP78S [GeForce 8200] SATA Controller (non-AHCI mode) (rev a2)
00:0a.0 Ethernet controller: NVIDIA Corporation MCP77 Ethernet (rev a2)
00:0b.0 PCI bridge: NVIDIA Corporation MCP78S [GeForce 8200] PCI Express Bridge (rev a1)
00:14.0 PCI bridge: NVIDIA Corporation MCP78S [GeForce 8200] PCI Bridge (rev a1)
00:18.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 11h Processor HyperTransport Configuration (rev 40)
00:18.1 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 11h Processor Address Map
00:18.2 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 11h Processor DRAM Controller
00:18.3 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 11h Processor Miscellaneous Control
00:18.4 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 11h Processor Link Control
02:00.0 VGA compatible controller: NVIDIA Corporation C77 [GeForce 8200M G] (rev a2)
07:00.0 Ethernet controller: Qualcomm Atheros AR242x / AR542x Wireless Network Adapter (PCI-Express) (rev 01)
mike@mike-Compaq-Presario-CQ60-Notebook-PC:~$

[also not sure how to /etc/apt/sources.list file, where software repositories are listed. As root, you can edit that file with a simple text editor to remove or remark out the reference to the disk. [sudo [editor name] /etc/apt/sources.list)
I that in the configure network devices connections.
Here is the Systems Report
System: Host: mike-Compaq-Presario-CQ60-Notebook-PC Kernel: 5.0.0-37-generic x86_64 bits: 64
compiler: gcc v: 7.4.0 Desktop: MATE 1.22.2 wm: marco dm: LightDM
Distro: Linux Mint 19.3 Tricia base: Ubuntu 18.04 bionic
Machine: Type: Laptop System: Hewlett-Packard product: Compaq Presario CQ60 Notebook PC v: F.34
serial: <filter> Chassis: Wistron type: 10 serial: <filter>
Mobo: Wistron model: 303C v: 08.48 serial: <filter> BIOS: Hewlett-Packard v: F.34
date: 12/23/2008
Battery: ID-1: BAT0 charge: 0% condition: 47.5/47.5 Wh (100%) volts: 10.8/10.8
model: Hewlett-Packard Primary serial: N/A status: Charging
CPU: Topology: Single Core model: AMD Sempron SI-42 bits: 64 type: UP arch: Turion X2 Ultra
rev: 1 L2 cache: 512 KiB
flags: lm nx pae sse sse2 sse3 bogomips: 4199
Speed: 1050 MHz max: 1050 MHz Core speed (MHz): 1: 1050
Graphics: Device-1: NVIDIA C77 [GeForce 8200M G] vendor: Hewlett-Packard driver: nouveau
v: kernel bus ID: 02:00.0 chip ID: 10de:0845
Display: x11 server: X.Org 1.19.6 driver: nouveau unloaded: fbdev,modesetting,vesa
compositor: marco resolution: 1366x768~60Hz
OpenGL: renderer: NVAA v: 3.3 Mesa 19.0.8 direct render: Yes
Audio: Device-1: NVIDIA MCP72XE/MCP72P/MCP78U/MCP78S High Definition Audio
vendor: Hewlett-Packard driver: snd_hda_intel v: kernel bus ID: 00:07.0
chip ID: 10de:0774
Sound Server: ALSA v: k5.0.0-37-generic
Network: Device-1: NVIDIA MCP77 Ethernet vendor: Hewlett-Packard driver: forcedeth v: kernel
port: 30f8 bus ID: 00:0a.0 chip ID: 10de:0760
IF: enp0s10 state: up speed: 100 Mbps duplex: full mac: <filter>
Device-2: Qualcomm Atheros AR242x / AR542x Wireless Network Adapter
vendor: Hewlett-Packard driver: ath5k v: kernel port: 4000 bus ID: 07:00.0
chip ID: 168c:001c
IF: wlp7s0 state: down mac: <filter>
Drives: Local Storage: total: 149.05 GiB used: 28.80 GiB (19.3%)
ID-1: /dev/sda vendor: Toshiba model: MK1652GSX size: 149.05 GiB speed: 3.0 Gb/s
serial: <filter>
Partition: ID-1: / size: 145.71 GiB used: 28.80 GiB (19.8%) fs: ext4 dev: /dev/sda1
USB: Hub: 1-0:1 info: Full speed (or root) Hub ports: 3 rev: 2.0 chip ID: 1d6b:0002
Device-1: 1-1:2 info: Realtek USB 2.0 multicard reader type: Mass Storage
driver: ums-realtek rev: 2.0 chip ID: 0bda:0158
Hub: 2-0:1 info: Full speed (or root) Hub ports: 4 rev: 2.0 chip ID: 1d6b:0002
Device-2: 2-2:2 info: Suyin Acer/Lenovo Webcam [CN0316] type: Video driver: uvcvideo
rev: 2.0 chip ID: 064e:a102
Hub: 3-0:1 info: Full speed (or root) Hub ports: 3 rev: 1.1 chip ID: 1d6b:0001
Hub: 4-0:1 info: Full speed (or root) Hub ports: 4 rev: 1.1 chip ID: 1d6b:0001
Device-3: 4-3:2 info: Apple USB Mouse [Mitsumi M4848] type: Mouse
driver: hid-generic,usbhid rev: 1.0 chip ID: 05ac:0301
Sensors: System Temperatures: cpu: 89.6 C mobo: N/A gpu: nouveau temp: 101 C
Fan Speeds (RPM): N/A
Repos: Active apt repos in: /etc/apt/sources.list
1: deb cdrom:[Linux Mint 19.2 _Tina_ - Release amd64 20190729]/ bionic contrib main non-free
Active apt repos in: /etc/apt/sources.list.d/official-package-repositories.list
1: deb http: //www.mirrorservice.org/sites/packages.linuxmint.com/packages tricia main upstream import backport
2: deb http: //archive.ubuntu.com/ubuntu bionic main restricted universe multiverse
3: deb http: //archive.ubuntu.com/ubuntu bionic-updates main restricted universe multiverse
4: deb http: //archive.ubuntu.com/ubuntu bionic-backports main restricted universe multiverse
5: deb http: //security.ubuntu.com/ubuntu/ bionic-security main restricted universe multiverse
6: deb http: //archive.canonical.com/ubuntu/ bionic partner
Active apt repos in: /etc/apt/sources.list.d/skype-stable.list
1: deb [arch=amd64] https: //repo.skype.com/deb stable main
Info: Processes: 149 Uptime: 1h 04m Memory: 1.70 GiB used: 757.9 MiB (43.6%) Init: systemd
v: 237 runlevel: 5 Compilers: gcc: 7.4.0 alt: 7 Client: Unknown python3.6 client
inxi: 3.0.32

´07:00.0 Ethernet controller: Qualcomm Atheros AR242x / AR542x Wireless Network Adapter (PCI-Express) (rev 01)´

´07:00.0 Ethernet controller: Qualcomm Atheros AR242x / AR542x Wireless Network Adapter (PCI-Express) (rev 01)´

Try this: Establish a wired ethernet connection. (If you don't have an ethernet cable handy, borrow one from a friend or pick one of at a store; they are inexpensive.)

Once you have a working connection, follow the instructions in this article regarding Ubuntu and its derivatives regarding "Additional Drivers": https://www.howtogeek.com/213488/how...vers-on-linux/

Let us know how that goes.

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