Hello and welcome to PCHF,
Not sure if we will be able to help you solve this problem but we can definately point you in the right direction.
I found a solution to that in other forums.This particular monitor has a 1KO
resistor that needs to be changed
If you have never fixed a monitor before then I suggest you phone around some computer repair companies and see whether they repair monitors.
Explain this problem to them.
When i hit the monitor it gets back to normal!!!??
This means that you monitor also has `dry joints`. These are easy enough to repair but once again it means you would need to open up the monitor and solder things.
Follow my above advice and phone around some computer repair shops and see whether anybody will want to repair it.
At the end of the day it may work out cheaper to purchase a new monitor compared to paying the labour for repairing your monitor.