If you've just installed new hardware, the
Blue Screen crash will probably be caused by an incorrect driver. Boot Windows into Safe Mode (by hitting F8 just before the Windows logo shows). In Safe Mode, you can go to Control Panel > System > Hardware Manager to roll back the driver or to uninstall the device.
Other causes are faulty RAM and bad capacitators (caps) on the motherboard. Though rare, I've also seen BSOD from a compuer trying to boot from a corrupt CD
.Most of the times
Blue screen of death is due to file corruption. Boot from the Windows install CD and go into the Recovery Console. From the command line run chkdsk /r to fix file errors. Once chkdsk is done, exit the Recovery Console and try to restart.