If as Bill2 says, you don't have deeper issues, to just get into safe mode when F8 won't work:
Start> Search Box> Type msconfig
In System Configuration window. Click on the Boot tab
Check the option titled Safe Mode. Minimal Safe Mode is the default Safe Mode option.
Click the OK button, you will be asked if you want to restart
Click the Restart button
After you are done, you can repeat and unclick the safe boot if necessary.