have you tried booting into safe mode?
also try booting to "last know good configuration".
as the computer boots, keep pressing on the F8 key.
if you are presented with the option of selecting a boot device, choose to boot from the hard disk.
continue pressing the F8 key until you are prompted if you want to boot into safe mode. choose to boot to safe mode.
see if safe mode will be able to run. if it does, restart the computer.
keep pressing on the F8 key again, and this time select to boot to the last known good configuration.
This is a link from Microsoft about Windows 7's Last known good configuration Using Last Known Good Configuration
i hope this helps, let us know of any updates, we'd be glad to suggest more troubleshooting options