If you can start it up in safe mode I would suggest a simple system restore.
Click Start, point to All Programs, point to Accessories, point to System Tools, and then click System Restore. System Restore starts.
On the Welcome to System Restore page, click Restore my computer to an earlier time (if it is not already selected), and then click Next.
On the Select a Restore Point page, find the last restore point where your computer worked and booted up correctly. And click next.
Let it do it's job, and you should be all ready to go :].