ate cheska the best solution u nid is to re-format your pc..i experienced that kind of problem too...i try to restore ... and remove my sql but when i re-install again my sql the same problem exist...so i did re-formatting and my server is okey now.... don't forget to secure all your important files before u re-format your pc....still consult an expert to be sure...
follow this steps: 1. Click Start 2. Program 3. Accessories 4. System Tools 5. System Restore 6. When System Restore Window appear choose Restore My Computer at Earlier Time and click next 7. Then choose the date before u install your SQL and Click next...u're PC will reboot just w8 until it finish...that's it....