When I try to save anything (document, audio file, whatever), my computer suddenly shuts down. No error message or anything, just a blue screen with white writing for a split second, followed by the bios screens you see when you restart. Any suggestions? I have plenty of hard drive space, I wonder if I've got some bad ram or something. Any tests I can run to isolate the problem? Thanks!

have a look at the event log and see if there is anything useful reported there related to the crashes Start >> Control Panel >> Admin Tools >> Event Viewer

Download and install Memtest86. Run this and it will run your RAM to the wall and tell you if it failed and where it failed.

Here's the errors I get in the event viewer: -driver cdudf.SYS has been blocked from loading -driver UdfReader.SYS has been blocked from loading -Error Code: 00000006, parameter 1 0000000, parameter 2 0000000, parameter 3 0000000, parameter 4 0000000

try http://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=0x00000006+%22WinXP%22 looks like its at microshaft windblowz to http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ddtools/hh/ddtools/bccodes_59k7.asp and scroll up twords the top on the left hand side and u will see bug check 0x6.