BleepingComputer.com: Over Frequency

Hi! hope somebody can help with this, actually it's from my friend's PC problem. It's just when he start-up his computer it goes well, but in the middle of his work his monitor's suddenly turn blackout the an alert pops up. It says "OVER FREQUENCY". Anyone can tell what's the with the PC? i hope anyone can help me because i'm not a techie guy i just want to learn and probably help my friend or maybe when my pc got the same problem. any suggestions?

Sounds like the screen refresh rate has been changed to something, incompatable with the monitor.
Try this:
Go into Safe Mode.
How to start Windows in Safe Mode
Control Panel / Appearance and Themes / Display / Settings tab / Advanced button / Monitor tab
Set the Screen refresh rate: to 60.
Apply / OK
Reboot, and see if that works.

Or, see if this helps:

WARNING:
This is a registry edit. If you're not comfortable with working in the registry, DO NOT ATTEMPT.
Improper changes to the registry could render your computer inoperable.
Remember to backup the registry before making any changes.
Instructions, on how to do that, can be found here:
How to back up, edit, and restore the registry

"Out of Frequency"