Can't access desktop files, also My Computer.

I can't access email (Thunderbird) and the Internet (Firefox). I can access Word and open the most recent files that way, but individual desktop files are locked somehow. I plugged in my portable hard drive and eventually My Computer opened it, but when I tried opening a file on the h.d. it wouldn't open.

This is a critical disaster as I have a Thursday noon deadline and am in the middle of composing my weekly essay on books as well as editing the Jan 1 edition of a Newsletter in which it will appear.

I've tried turning off the computer and letting it rest for 20-30 minutes, but with no result.

The computer is HP a1550y, with XP Home OS. Word is 2003 version with Service Pack 3.

Help!!!