I've had my case open for eaons as the hard drive cables get a bit crushed and I kept meaning to pick up some air to dust the heatsink. It's been running OK. Today got the air. Dusted my daughter's computer and mine. Went to put the cover back and sure enough the hard drives were not detected. Cover off, push everything back in start it up all ok. Got my husband to cut a hole (stop laughing) in the cover panel and fitted a plastic clamshell in to leave room for both the hard drive cables. Put the cover back on. Boots into windows xp and freezes with the floppy locked up (light on nobody home). So I reboot and go into the bios to see if something there is messed up. I changed some setting, I don't even know what. Do save and exit. Nothing. Reboot. Nothing. Change the Cmos jumper to reset. turn on and turn off computer. Move jumper back, reboot, nothing. Take out the battery and pop it back in. Reboots to default bios settings. Change the date and a few settings to where I know they should be. Exit and save. Nothing. Reset the bios again with battery removal. Reboot and enter Windows everything works fine, run System Mechanic 6. Everything looks fine. Ram is set too slow (100mhz instead of 166 where it was, its PC 3200). Run PC care, which changes some settings to optimize performance and reboot. Nothing. Reset again. Enter Bios and change just the date. Save and exit. Nothing. I tried changing the CMOS battery and nothing changes. The slightest change to the bios results in the inability to boot. Any ideas. AMD Athlon XP 2800 running Windows XP with sp2, Bios updated in 2005, Computer is about 3 years old with an FIC au 31 motherboard, NVidia 6200 AGP video card, a WD 160 GB and 40 GB hardrive, a powerup 400 W powersupply, Lite-on CD RW and a Nec DVD RW.