My monitor starts to flash big bold vertical lines like a full screen colour, barcode. If I switch the monitor off for a few seconds it stops but comes back after about twenty minutes. Any clues please.

Hi Errie, welcome to the PCHF!

Generally when that happens - the monitor is only on the way out...Make sure where your monitor is located, is adequatley ventilated...

Also, make sure there is no dust in the vents at the back.

Samsung Flat Panel Syncmaster 193v

Sorry you must think me awfully rude. Thanks for quick reply

Monitor is new, replaced under warranty and new cable.. Monitor test shows Good. I have double checked all the settings like resolution etc and all are default. Done temperature tests, computer is clean inside, reinstalled all drvers and all report enabled and working properly. I did have an old CRT monitor which I ran for a while and the flashing did not occur even if I ran it for hours on end playing Serious Sam on the mental level.

Hrmm....

Just another quick question...once the lines come up, restart the computer...do the lines still appear in bootup? It sounds either like the monitor, or the video card...might be the video card overheating...