Hi Dan,
do you have the install disk? If so I'd recommend booting from that and click repair on the installation screen. Failing that you could try system restore or pressing F8 when booting, like into safe mode, but choosing 'last good known configuration'. If you get into Windows try running the system file checker by right clicking cmd prompt and run as admin. Then type:
sfc /scannow
Press enter and let it run through. If you still get blue screens see our blue screen section and read the sticky on how to post the information.