The System Restore tool built into Microsoft Windows allows you to dial the operating system back to an earlier time without deleting any of your files. The Dell OptiPlex 755 has a few features that can affect a restoration to your system and get you running again if your system is not behaving as it should. Use the Dell PC Restore tool is a last resort option, as the operation wipes all the data on your computer and returns it to its original condition.
Click "Start," "All Programs," "Accessories," "System Tools" and "System Restore."
Choose "Restore my computer to an earlier time," then click the most recent date on the calendar in bold print. Select a restore point from the list, then click "Next."
Accept the warning and click "Next." The restore process restarts your computer; check to see that the problem is solved after the computer restarts. If not, you can restore back further. Follow the steps again, going to the next most recent restore date, until the problem is resolved.
Power off the computer. Turn on the computer, and while it's booting, hold down "Ctrl" and press "F11" in Windows XP or "F8" in Windows Vista or later.
Click "Restore" then "Confirm" in Windows XP. In Windows Vista and later, click "Repair your Computer," then "Next." Log in with a username and password. Click "Dell Factory Image Restore," then "Next." Confirm that you want to reformat the hard drive, then click "Next."
Click "Finish" when the button appears. Your computer reboots, with the operating system now restored to the same state it was in when the computer was new.