fix computer errors

I have a custom built computer with the following applicable specs:
- 2.3ghz AMD dual core processor
- 4GB of DDR2 800mhz RAM
- Nvidia 8800GTS
- Windows XP Service Pack 2
I recently have been having a blue screen error that I nor my boyfriend can figure out. Upon starting up the computer, everything will load, Windows will start, it goes to the Welcome screen and then blue screens. The blue screen only flashes for an instant and the computer reboots. It will do this over and over again. Sometimes, if I let it go, it will eventually start up. Of course, the “critical error in Windows” message will come up. When checking the data for the error, it states:
dcom 10005 system service control manager, 7001, service control manager 7026
Also, it states that the error occurred in sptd.sys (and the file has been dumped)
I did research on sptd and found that it is a system file for Daemon Tools. I’ve never downloaded Daemon Tools nor ever had it on my computer. Also, we tried doing a system restore to 3 weeks ago, it still blue screens. I installed 2 more GB of RAM (to bring it to 4GB) a few weeks ago but even after taking the new sticks out, it still blue screens.
Also, I reset the computer to default settings in the BIOS as a last ditch effort. Still no dice.
I can’t figure out the problem. Any help would be greatly appreciated, thank you!