Hi A,
I'm so sorry that you've run into trouble with your system, and subsequently with ArcToolbox. Unfortunately, the best advice that I can think of is to reinstall ArcMap, although I totally understand your worries about being able to reinstall with your student license. If the only tools you're having trouble with are python scripts, you may want to try reinstalling Python itself...but that will only be helpful if the problem is isolated to python scripts (and even then, its just a shot in the dark). I think you're best bet may be to try and call tech support to see if they have any ideas about what you can do.
Sorry I couldn't be more helpful!
Lauren Rosenshein
Geoprocessing Product Engineer