I've made a little progress in the above respect, but my knowledge doesn't stretch far enough to know which direction to look in next. I had a problem with my fullscreen apps, such as games, just shutting down unexpectedly without error messages or hanging, nor any message in the event log. They would just dissapear. This developed into the entire computer powering off completely, with the exception of the power light. No fans... Nothing. I couldn't get out of this by restoring my system from an image, which had all my drivers installed (including an old version of the forceware), even after I replaced my Gforce 440MX AGP graphics card, with my old Voodoo5 PCI card. Since then, I have re-installed completely from my XP disc, using only my Voodoo5 PCI card. I have had no problems on that setup. Yesterday, I tried my Geforce card again, and installed the newest forceware. My PC booted up, and powered off straight away, as expected. I removed the geforce card, and powered up on my vodoo. I then successfully booted the pc. However, when I ran The Sims for my girlfriend both at 1024x768 and 800x600, it simply crashed out without warning, or in other words, I had the original problem again. Happily, this time, unlike before the full re-install, I had System Restore turned on. I chose the last restore point before installing the Geforce AGP card, and now I once more have no problem at all. Options seem to be.. 1, My Geforce card is damaged 2, My AGP slot cannot supply the card with enough power, or some such failure 3, The drivers screw up my machine, which seems unlikely. They worked before. 4, After trying to use my Geforce card, something changes on a software level causing me a problem with full screen applications, as corrected by a system restore. If anyone has any suggestions or pointers, I'd be most interested .