When the computer is first starting start tapping F8. Hopefully a similar to the one below will appear. This is the Advanced Boot Options page. If this opens use the up and down keys to navigate to Safe Mode and press Enter.
If you can boot into Safe Mode try doing a System Restore.Start> All Programs> Accessories> System Tools> System Restore
When this opens make sure that "Restore my computer to an earlier time
" is chosen, and click on Next>
The dates appearing in bold are the dates that you can restore to, click on the date that you want and then click Next>
to start the System Restore. This may take a long time to complete, and when it is done it will restart your computer. When the computer restarts and you have logged on as the administrator a Restoration Complete page will appear, click on OK
to complete the process.