Are you able to boot into Safe Mode? If so, check your event logs (Start > run > type "eventviewer.msc" without the quotes). Go to the 'System' section on the left, and check for any thing like "dump log" in the description, or anything that sounds like an error description, and check to see if that's the BSOD. If it is, give us the error code, and possibly look to see if you have any minidump files (usually in C:\Windows\Minidump).