Linux Mint 20.1 Mate installed this fstab file on my Lenovo 420T Laptop. Even on the install Live USB Flash Drive I cannot access the Windows folder on the C:\ drive. Only when I am in Windows 10 is it possible to access the Windows folder.

# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point> <type> <options> <dump> <pass>
# / was on /dev/sda5 during installation
UUID=c74d116c-ae0f-4cfb-9845-a8b3f5ff4230 / ext4 errors=remount-ro 0 1
/swapfile none swap sw 0 0
LABEL=Windows7_OS /mnt/Windows7_OS auto nosuid,nodev,nofail,x-gvfs-show 0 0
LABEL=Local\040Disk\040D /mnt/Local\040Disk\040D auto nosuid,nodev,nofail,x-gvfs-show 0 0
LABEL=SYSTEM_DRV /mnt/SYSTEM_DRV auto nosuid,nodev,nofail,x-gvfs-show 0 0

Continuation of Reply above: This notification is displayed:

Sorry, could not display the contents of "Windows". Error when getting information for file /mnt/Windows7_OS/Windows/"notepad.exe" input/output error.

I've tried another distro and the same notification appears.

Post the output of the command:
lsblk -f

moshe@moshe-ThinkPad-T420:~$ lsblk -f
NAME FSTYPE LABEL UUID FSAVAIL FSUSE% MOUNTPOINT
sda
├─sda1
│ ntfs SYSTEM_DRV
│ 30984D50984D162E 5.5G 11% /mnt/SYSTE
├─sda2
│ ntfs Windows7_OS
│ 01CFCAA927923210 44.6G 62% /mnt/Windo
├─sda3
│ ntfs Local Disk D
│ 60723F91723F6B44 114.8G 53% /mnt/Local
├─sda4
│
└─sda5
ext4 c74d116c-ae0f-4cfb-9845-a8b3f5ff4230 64.3G 28% /
sdb iso966 Linux Mint 20.1 MATE 64-bit
│ 2021-01-03-17-46-14-00
├─sdb1
│ iso966 Linux Mint 20.1 MATE 64-bit
│ 2021-01-03-17-46-14-00 0 100% /media/mos
├─sdb2
│ vfat C26E-047E
└─sdb3
ext4 writable
79cafbd5-2c04-433a-a5c8-14b38acffb38 5.1G 0% /media/mos
sr0
moshe@moshe-ThinkPad-T420:~$

Ok, they are mounted as posted.

What do you mean by cannot access?

What happens when you try accessing the filesystems from a file browser, from a terminal window?

Continuation of Reply above: This notification is displayed:

Sorry, could not display the contents of "Windows". Error when getting information for file /mnt/Windows7_OS/Windows/"notepad.exe" input/output error.

I've tried downloading and installing:
Samba
caja sharet
But it hasn't solved the problem.

I assume Windows runs ok and that if you run notepad it works as expected?

michaelk yes Windows 10 and notepad works OK. Other folders in both the C:\ and D:\ drives open without problems.