Installed Ubuntu 10.10 on a hard drive by itself (no windows). All updates are up to date. Everything`works fine except when I plug in a 320 gig Toshiba external hard drive....it is not recognized. When I plug in an 8 gig flash drive it is recognized no problem.

What do I mean by "not recognized"? I mean: how do you know it was not recognized. You can check the command "cat /proc/partitions" in a terminal with and without the hdd attached. If you see some difference, it's ok. If the difference is something like "sda1" (sd+letter+number) then you have partition on it, maybe it can't be handled in Ubuntu (no filesystem on it or so). If there is only "sda" in the difference for example (sd+letter, but no number after it) then the drive itself is detected, just no partition is created on it. Also you can check out the messages of the kernel, with the "dmesg" command in the terminal. If there is no disk/partition/anything in /proc/partitions, there can be an USB level problem, you can issue command "lsusb" as it was suggested before my answer. It's really matter of what do you mean about "not recognized".

@Marco Ceppi @Oli @Pitto By "not recognized" I meant that when I plug in a 8 gig flash drive an icon immediately appears on the desktop imdicating that there is a flash drive plugged in and I can click on it and view the files on the flash drive. It also shows up on the "Nautilus" default file manager. When I plug in the 320 gig Toshiba external hard drive, I get no indication on the desktop or the file manager (thus "not recogized").

When I run the command cat/proc/partitions/ I get an error message

Could not open location 'file:///home/bob/cat/proc/partitions' 

with or without the external hard drive installed. With the dmeg command I get about 10 pages of info with no mention of disk/partition/anything in /proc/partitions.

When I run lsusb command I get the following:

bob@bob-desktop:~$ lsusb
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 003: ID 04b3:3003 IBM Corp. Rapid Access III Keyboard
Bus 003 Device 002: ID 04b3:3004 IBM Corp. Media Access Pro Keyboard
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub