A Windows 7-based computer doesn’t start because the master boot record (MBR) has been corrupted. When you try to use the Startup Repair tool to fix the MBR, the Startup Repair tool reports that no problem was found.
When a USB flash drive is inserted in a computer, the computer hardware sometimes reports that the USB flash drive is the system partition. The Startup Repair tool examines the USB flash drive instead of the actual system partition on the hard disk. Because Startup Repair cannot locate the corrupted MBR, it does not detect a problem.
To avoid this behaviour, remove the USB flash drive before you run the Startup Repair tool.
If you do not have a USB flash drive then disconnect any external disks you have attached to the computer.
If the problem persists see Advanced Startup Troubleshooting in Windows 7.
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