Remove the cable and check for any bent pins in the connector and then reattach firmly and test again.
Also check if the front buttons has a degaussing feature and run it.
Check for any updated drivers for your video card.
Finally test the monitor on your other PC and try the other monitor on this PC.
If the old monitor acts up on the other PC change a new Monitor
Win 98 and a 15 inch monitor. This is a second computer and is only used to play games. The monitor screen changes colors on its own. Is this a sign that the monitor is quitting or what ???? Thanks