Do you hear the high-pitch wine of the high voltage circuit (all CRT's, i.e. monitors and TV's make this noise, it's just the way they work)? Does the screen make a that static crackle sound when you power it on or off? If not, I'd say your flyback transformer went out, or the high-voltage power transistor. A failure of either is unfortunate since they are hard to get replacements for, and difficult, not to mention very dangerous, to replace.

But, before you go buying anything, make sure a cable did not come loose. After 20+ years, connectors are very prone to being dirty and not making good connections any longer. Reseat all connectors you feel comfortable working with. If you don't know much about electronics, then get help from a friend who does, otherwise STAY AWAY from the monitor! The high voltage is totally in the open in coin-ops and it will reach out and bite you.

If you determine for sure that it is a monitor problem, you can buy new and refurb units for a few hundred last I checked. Might be worth it if the CRT has any bad screen burn, since that is not something you can fix. At the very least you are going to want to do a cap-kit on the monitor as part of your restoration.

Matthew