Do you know which
driver you installed that is preventing Repair?
Did you allow Startup Repair to use System Restore if it asked, since that should have overcome the bad
driver if it was recently installed.
Boot the Windows 7 DVD Repair console or Repair CD, accept any offered Repair, then if it doesn't start boot back in to Recovery Tools list to run Startup Repair again, accept System Restore. If it still doesn't work, run System Restore from the Recovery Tools list.
System Repair Disc - Create System Recovery Options