If you are getting a blue screen of death as your system tries to boot into Windows 7.
The BSOD error code is will be STOP 0x000007b.
In order to fix this you need to load your bios system control panel (while booting press del. or F2 [depends on every system])
Then you need to check which HDD you are using?
And check if you have you changed the SATA mode from IDE to AHCI?
If yes, you need to change it back to IDE.
For more information check out this link: http://support.microsoft.com/kb/922976