If you don't have a Win7 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 WIn7 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 Win7 disk then from the Disk tab chose Rebuild MBR, Apply.
If this fails then boot the WIn7 repair CD to try the Repairs again three times with reboots or until Win7 starts..
Next boot back into PW CD to change the Active partition (using rightclick>Modify) to the Win7 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 Win7 DVD or find one for your version for Reinstalling Windows 7.