Computer crashes

[lena]

I run Windows XP Pro(not SP2) on an Acer laptop (1.4Ghz, 256MB). Since I started using UR heavily, I have had two major computercrashes, that I never had before (I have had this computer for more than two years). I could not do anything, even ctrl-alt-del did not work anymore. I had to hard reset the computer using the power button. Normally my computer is very stable. The worst that happens is a single program that does not respond, after I close that everything works again.

The other programs I have constantly open are Firefox (1.0), Picasa (2.0) and Putty.

Does anybody else have this experience? The crashes do not happen when I am actively doing something in UR, the active program was Firefox. I can very well imagine the problem lays with Firefox, but then it is strange that it did not happen before, I have been using Firefox for a long time now.