I belatedly learn that my daughter's Dell E510 has occasionally been failing to open folders or software. Tonight it suddenly gets past the XP splash screen and hangs, that is, after the splash screen, the screen goes blank with the pointer in the middle of the screen and that's all. The four Dell diag lights are off. The HD sounds like it's spinning up when we power on, but after a while, all is silent except the psu fan. I ran the quick diagnostics and HD diagnostics with no notable results. We took the two 1 GB RAM blades out in different combinations, but it didn't help. We took out the GEForce GT8800 and replaced it with the original video card but it didn't help. We disconnected all the usb devices but it didn't help. We took out the battery on the motherboard and then put it back in (haven't had time to buy a new one yet). We fiddled with all the power cables and connections. The after market PC Power and Cooling PSU seems okay, that is, the fan is running. I put the Dell installation disk in and booted to it and let it run through the XP setup, but on the required restart it just hangs again. I'm running the extensive testing in Dell diagnostic now, but it's past all the memory tests without any notable results. Any ideas? Is the hard drive dying/dead? How would I know? Is the motherboard dead? How would I know? Doesn't sound like a software/virus issue but who knows. She had a booger of a trojan last year, and we had to blank the HD and start over. Don't wanna do that again. Thanks. Since first post, did safe mode boot and it stopped at mup.sys, which I think I know may or may not be a software problem, or could be a million other things. any suggestions appreciated.