Do you ever get an "SCSIPORT.SYS" error? This is common with conflicting hard drives. From my experience you may need a clean install of the OS. If you don't have a CD you should be able to get a copy from Microsoft. If at all possible, get an external HD and save as much data on there as you can.
Oh, did you upgrade anything? New motherboard? etc.. Are you running anything from Daemon tools? They seem to cause the BSOD sometimes.