I recently switched to linux (just yesterday to be exact) and i was trying to set up an external drive and it didn't show up on the desktop when i plugged it in. i did some looking about my problem and a certain post said to run the following code in terminal, "sudo fdisk -l" so i did and this is the response it gave me.
(name removed)@Desktop:~$ sudo fdisk -l

Disk /dev/sda: 200.0 GB, 200049647616 bytes
255 heads, 63 sectors/track, 24321 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x1549f232

Device Boot Start End Blocks Id System
/dev/sda1 * 1 23971 192547026 83 Linux
/dev/sda2 23972 24321 2811375 5 Extended
/dev/sda5 23972 24321 2811343+ 82 Linux swap / Solaris

Disk /dev/sdc: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000000

Disk /dev/sdc doesn't contain a valid partition table
(name removed)@Desktop:~$

the first drive it mentions is the one inside the computer running ubuntu and the second one the 500 GB drive i can't seem to get into.

Seems to me you need to format the drive
You can use gparted

My experience with my external USB HD is that I have to connect it to the ports on the back of the PC and can not use an USB extension cable.

This is an external disk without external power supply and the conclusion is that the there is to much 'power' loss when adding extra cabling (extension or front USB ports). This might be the case in your situation as well, just check.

repo was correct and after getting Gparted i was able to reformat the drive and it worked, it is now showing up on the desktop. thanks for the quick response.