Acadia,
You're using Windows XP, aren't you? I get the "High speed USB2 device in a legacy USB1 port" nonsense very often in XP Pro (and all I can do is reboot); XP's USB drivers are very buggy. :-(

In your case, reinstalling the OS is the best solution. It is possible your external drive is okay, but your computer just can't see it anymore, because of an USB driver breakdown.

cedarwolf,
Chances are the same applies to you; Did you try to plug your USB drive into some other computer? If other computers see it, the problem are your USB drivers.

The only solution for USB driver hell is upgrading XP to Win2000... :-D Win2000's USB drivers are rock solid. Military grade stuff...