it will go off unless I'm using the mouse.
Normally I would have said PSU issue with your VDU switching off after 10 secs but the "
unless I'am using the mouse" statement is confusing ?
I'am assuming you have not changed any of the VDU settings recently, even then, I don't think that you would be likely to set the "inactivity sleep" timer to 10 seconds, again assuming the VDU has such a feature.
If your VDU has a separate PSU try substituting that if possible with a unit of similar voltage/power rating with a similar connector of the same polarity.
If the VDU PSU is integral then your only option is to get inside the casing and look for any obvious, faulty components such as leaking or swollen electrolytic capacitors.
I had exactly the same issue recently with a much younger Samsung VDU, just out of warranty of course !
This had an external PSU which I was able to directly substitute, like for like, unfortunately that did not cure.
Did manage to open the VDU but could not see any obvious component failures, no joy, had to scrap.
9 years is quite a long life for a modern, "
economy" electrolyitic capacitor, the component that is most likely to age and fail most quickly.