The system software is important! As you can see in my sig, I got a new laptop and I loaded XP. The drivers disc that came with it had a System Software driver/software. It's description had something about comaptibility, yada yada yada, then support for USB Devices. Try that first before anything else, as it's the easiest (I believe).

Considering the drive has worked before, there is a chance that something on your system is corrupted and is not letting the drive work, say, the USB drivers.

You said previously that your BIOS was A00 right? I found an update to A08, so that may help.

By the way, I'm not clear on this, is it that no USB device works in any USB port?

BIOS file location: http://ftp.us.dell.com/bios/A08_1520.EXE

Other files that may be of help:
System Software: http://ftp.us.dell.com/utility/R143625.EXE

If that doesn't work, chat with a Dell Technician and see if they can be of any assistance.
Dell - Hardware Chat

At the last resort, you may want to backup all your data and reinstall Windows to see if that helps. You can also install a second copy of Windows on a split partition so that your current data remains intact. Try the suggestions above first. If it doesn't work, reply and I will post instructions to try and reinstall Windows, on a separate partition or overwriting your current installation (you will lose all of your data) if you would like.

I wish you a lot of luck and I hope your problems will be fixed without much hassle.

You can only chat to dell online support if your Laptop is still under warrenty, I would do what kevinzheng.101 says update your bios, and see if that works if not you could try a 'System Restore' and if that doesnt work you could put the resource cd in to run diagnostics, and as a last resort a reinstalation of your PC may be needed.

Thanks,
Seywar