Have you tried using RESTORE to go back to an earlier time ?
Download BELARC (try Google)and print out the text,this will include all your software keys.
I assume the license is a piece of software,why can't you save it to a USB or Floppy drive.You could try a registry cleaner,but--you may do more harm than good.
You could go in to the registry and search for all references to SOLIWORK and delete them- again at your own risk.
As has been said on a number of occasions,unless you are 100% sure 'Do not mess with the registry'