I am running a fairly new (August 2005) custom built pc. It has two harddrives (20GB and 120GB). The 20GB harddrive is my boot drive and the 120GB is used for the majority of the programs. Last night I was using up 97 of the 120GB. When I logged on today around 8:45 am (central) I had 450 mb left. I wasnt logged on over night so there is no reason for this. I found the folder that had gained size and opened it. An error message appeared that stated Windows Explorer is not responding. So i clicked on it then explorer started again. Every time I accessed that folder I just got a glimse of the contents (what I saw was normal, my music collection) then explorer stopped responding. I tried 3 times. So I tried to add another harddrive (a spare I have laying around) It works fine in this computer but when it was in the new computer the computer wouldnt boot. So I removed it. Wouldnt boot. I tried my harddrive with linux on it. It wouldnt boot. I tried this hdd as the master and it wouldnt boot. So as you can tell its not a hard disk problem. This is what happens in order 1: nVidia Graphics card bios displays (normal) 2: Phoenix bios displays (normal) 3: The page that shows the installed hardware (ram, hdd and cdrom drives) displays (normal) 4: Windows XP Home begins to boot 5:At the end of the boot cycle a blue screen flashes for less than a second (the severe error screen not the memdump) then my computer restarts. The second time I tried inbetween 3 and 4 it asked me how I wanted to boot and I chose safe mode. Didnt work. Does anyone have any suggestions? My friend and I think its a mobo problem. Specs: Windows XP Home Service Pack 1 20GB master hdd Samsung 120GB slave hdd ECS NFORCE4-A939 motherboard Athlon 64 3200+ 939 processor nVidia's Geforce 6600 256mb PCI-x16 graphics card NEC DVD-RDL burner Samsung CD-RW drive Nothing is overclocked.