sashijoseph
In the zone
ha ha thanks for reminding.I almost forgot!
OK,more seriously,first do the routine stuff......change resolution,refresh rates,remove and replug the monitor cable,update your graphics drivers,swap the monitor with a friend's...blah,blah,blah.
But honestly,I think you'll need to get inside the monitor.Check components of the rgb driver/output stage and the blanking circuit;the board on the neck of the crt.Check voltages, dry solder joints,reseat connectors etc.
If the lines are fairly uniform across the screen I suspect they could be retrace lines(though all 3 primary colors are uncommon),that's why I sugested the service centre.But of course first swap with someone's monitor and confirm.
Hope this helps.