Reboot. As soon as the system gets past the POST, start to tap the F8 key. You will get to a screen with several boot options - choose the one that says: Disable Restart on Error. Now reboot. You should see a blue screen error message. Post that ENTIRE message here.
Also, you can download a boot time anti virus utility (Avira, Avast, Bit Defender), create a bootable cd, and run that at system start.