Iwant To Make My Wishes About End Of My...
Law3 mins ago
No best answer has yet been selected by dotjhawkes. Once a best answer has been selected, it will be shown here.
For more on marking an answer as the "Best Answer", please visit our FAQ.Sounds like a defective component or solder joint. When it heats up the expansion can 'make good' a failing solder joint. An 'ageing' or failing component can also work once it's warm.
If your practical enough with a soldering iron you could have a peek inside but DON'T if you are unsure as there are lethal voltages inside VDUs.
Also worth checking the seating of the video card in the PC (if it's a separate card), and the security of the VGA cable to the PC.
Depending on the age it may be worth getting it repaired but the price of VDUs and flatscreens probably doesn't make it economicably viable.