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Windows 7: Boot cannot find OS "no valid partition"

05 Apr 2011   #1

Win 7 professional 64
Boot cannot find OS "no valid partition"

Had the problem before that was solved, but it has suddenly returned. I can't believe it is related, but my wireless keyboard transmitter died. I used an old USB keyboard, and when I started up no OS was found.

Hitting F8 brings up a DOS window I had never seen before. It asks on which hard drive to look for the OS. When I select C, it finds the OS the machine then boots fine. Shutdown and restart and it again can't find the OS.

Disk manager shows both hard drives as active. "Mark partition Active" is grayed out in both.

I have run Startup repair many times. It always results in:

Root Cause found
The partition does not have a valid system partition
Repair action: Partition table repair
Result: Completed successfully.

Then running it again it finds the same error.

the old thread on the problem here: No OS on restart as comp tries to boot from USB drive.

Attached Thumbnails
My System SpecsSystem Spec

05 Apr 2011   #2
Microsoft MVP


Make sure Win7 HD is set as first HD to boot in BIOS setup, after DVD/CD drive.

How and why did D Data drive become marked Active again? Mark Inactive: Partition - Mark as Active - Windows 7 Forums

See if these steps suffice. If not, boot Win7 DVD Repair console or Repair CD to Startup Repair - Run 3 Separate Times - Windows 7 Forum.

If this fails, unplug D drive and run Repairs again.

You can mark Inactive using free Partition Wizard bootable CD for a graphical interface, then run Rebuild MBR from the Disk tab which may preclude the need to run Repairs.
My System SpecsSystem Spec
05 Apr 2011   #3

Win 7 professional 64

Thanks for the reply. Tried to follow instructions, didn't go as expected but suddenly everything is working right.

I download the Partition Magic minitool was able to mark the D drive inactive. Machine restarted. Booted from Minitool boot disk, hoping to rebuild MBR. After choosing resolution I got the error "This bootable CD does not support Windows server". Huh? I have Win7 Pro 64 on the Machine. Anyway, shutdown and restarted a few times and everything worked.
My System SpecsSystem Spec


 Boot cannot find OS "no valid partition"

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