You should boot the Windows 7 DVD Repair console or Repair CD to run Startup Repair
. All bootrec, bootsect and other repair commands, tests and fixes are automated in Startup Repair. Run it several times then post back what it reports.
Next make sure Windows 7 or its 100mb System Reserved partition (preferred) are still marked Active: Partition - Mark as Active (Method Two)
. You can also use free Partition Wizard
bootable CD to mark Active, then click on HD to highlight it, from Disk tab select Rebuild MBR, Apply steps, reboot. This may preclude the need to run Startup Repair.
If these repairs fail then after confirming HD is good you'll need to run full Factory Recovery from its partition at boot, or from Recovery disks you have made or order. Or find a Windows 7 installation DVD to clean reinstall using the Product Key on COA sticker: Reinstalling Windows 7