Running a diagnostic Check

I am trying to figure out what exactly is making my system run so poor. It will run in safe mode fine, but not in the regular start up. I hit F8, then I select safe mode. All is fine. Then when I go out of safee mode it freezes. I am wondering if Iam doing the correct thing here. I tried to run the “safe mode for networking” but the system locked up anyway. I also tried the “go back to the best known configuration” (or something like that) but it locked up instantly…. I cannot get this thing to stop freezing. I installed a new video card, which was the problem. OR, So I thought…..need help here.