I have had to do a clean reintall of vista 64bit due to a virus.
Now i can never just boot up my pc i have tried everthing i can reformatted, deleted the partision reintalled. over 5 times now.
but same ever time the only way to reboot is keep trying untill get lucky. that mean using the restore, the repair, on vista disk even tried command prompt to rebuildbcd.
Even tried bootrec rebuildbcd
again nothing works soon as turn off back to same problem etherjust turns it self off or some times comes up with bootmage missing, CTR+ALT+DEL to reboot
some time get windows up only for it to turn it self off.
I would suggest low level formatting the HDD. Some Viruses have the ability to linger after a reinstall ready to mess with your new install. Another possibility is to take the HDD and scan it using another PC. That option is not without risk to the PC you are using to scan with however. If you have another HDD try installing on to that to determine if the issue is your current HDD or if the issue resides in other components in your system.