If Windows Vista or Windows 7 won’t start, you can boot from the system DVD and perform a System Restore to return your computer’s configuration to an earlier state. This is a great way to undo recent problems with malware,  spyware, and viruses.

Before doing a System Restore, I’d try running Startup Repair. Then, do this:

1. If you’re using Windows 7, your computer might automatically prompt you to perform a Startup Repair or to load the Windows Recovery Environment. Do this first. If it doesn’t work, continue following these steps.

2. Restart the computer from the Windows Vista or Windows 7 DVD (the computer must be configured to start from CD/DVD), and start setup.

3. When prompted, click Repair your computer.

4. Startup Repair will automatically detect a problem. When prompted, click Repair and restart, and then restart your computer from the Windows DVD. If Startup Repair does not automatically detect a problem, continue to the next step.

5. When prompted, click Repair Your Computer.

6. Click System Restore from the System Recovery Options.

7. Follow the prompts that appear to restore your system configuration to an earlier state.

8. When prompted, remove the Windows DVD and restart your computer normally.

If the problems still don’t disappear, you can repeat the process and choose an earlier System Restore date. If it still doesn’t work–I hope you made a backup! If so, you can restore your computer from a system image.