If you don't have a Windows 7 DVD, it's best to download and burn a Repair CD so the repairs don't depend on possibly corrupt System files. System Repair Disc - Create
From the System Recovery Options
run Startup Repair repeatedly. If Windows 7 won't repair, make sure the 100mb System Reserved partition (if you have it) is marked Active using free Partition Wizard
bootable CD, highlight the Windows 7 disk then from the Disk tab chose Rebuild MBR, Apply.
If this fails then boot the Windows 7 repair CD to try the Repairs again three times with reboots or until Windows 7 starts..
Next boot back into PW CD to change the Active partition (using rightclick>Modify) to the Windows 7 partition itself, try Rebuild MBR, if it fails then run the 3 repairs again from Repair CD.
If no installation shows to repair you may need to choose the CD Command Line to run bootrec /fixboot
and bootrec /fixmbr
to jumpstart it to appear.
You can copy out your files using the Repair CD this way: Copy & Paste - in Windows Recovery Console
or using Paragon Rescue CD freeware.
then run full Factory REcovery from boot or Recovery Disks, or use your Windows 7 DVD or find one for your version for Reinstalling Windows 7.