If your Windows 7 happens to be stuck in Startup Repair, where allowing it to repair your computer still results in going back to Startup Repair, and restoring a restore point doesn't help either, you could try to manually restore the Windows Registry to the last known good configuration.
Allow your computer to boot into Startup Repair, but rather than letting it perform the automatic repairs, click to go to the System Recovery Options menu. From there, you can open a command prompt.
Locate the system drive: this is usually the C: drive, but if not, navigate to other drivers and look for folders like Program Files, Users and Windows.
Once you've found the correct drive, navigate to the folder \windows\system32\config. Verify (using dir) that the following files and folders exist in there:
Create a backup of these files to a new folder (you have to create that as well):
MD MyBackup copy *.* MyBackup
Next, look in the subfolder RegBack and see whether the same files exist in there. Windows occasionally takes a backup of the registry in that folder. But take care: the files should be at least a few hundred KB or even several tens MBs, even up to a hundred. If any of these files are zero, do not continue the process as this is not a valid backup. You can also verify its age by looking at the timestamps (output of dir).
If the files look valid, you can copy these to the original location (\windows\system32\config):
copy *.* ..
If you are prompted to overwrite, do so for all files.
Close the command prompt and click Restart to reboot your computer. If the backup was valid and there are no additional problems, the system should boot normally. Note that you may have to reinstall certain programs and/or updates, if the backup was a bit older.