CAUSE: The BIOS can not access the boot device and this is due to a change in hardware or software.
SOLUTION: Since the problem is Windows startup then proceed to repair it.
Repairing the Windows 7 boot:
1- Insert the Windows 7 DVD in the CD-ROOM.
2- Choose the Language.
3- Choose "Repair Your Computer"
4- Choose "windows 7
5- Select "Startup Repair"