People having fatal problems with their PC's after installing SP2 are a very small minority.
Considering that SP2 is a service-pack and not a regular update, I would assume you had read the release notes that came with it. If not, well, hopefully you won't fall into any more holes on your own accord once we dig you out of this one.
For now, post us some specs on your box. Software too, as something in there may be causing a conflict. Lastly, a trip to the Microsoft troubleshooting pages and forums would be advisable in helping you identify your problem, though we will certainly do what we can to sort you out (if possible).