Does anybody know how to fix a Williams Moon Patrol arcade cabinet when it gets this screen after turning on?

This is my Williams arcade game, Moon Patrol.  It worked fine when I picked it up a few months ago, but one day in July it started showing this screen after it had been on for only a few minutes.  I haven't had time to check out the internals since it started doing this, but I plan to get inside the cabinet and reseat everything in the hopes that maybe one of the chips isn't sitting right thanks to heat & humidity.

I've only opened it once before, and that was to try setting the dip switches to allow free play while also permitting attract mode to keep running - by default entering free play doesn't display a preview of the game, which I really wasn't too keen on.  Lucky for me, the previous owner had already installed a button to the right of the coin slots and added a wire to the coin mechanics - it just needed to be reconnected to the button.  This way nobody needed to access the coin mechanics and I could keep it closed, avoiding potential damage (I've got four daughters, and the two youngest are not exactly good at handling things carefully - it's a good thing these were built with abusive teenagers in mind)

I'm posting this in the hopes that someone out there has run into this issue and has more information on what might specifically cause it to happen, on the off chance that reseating all the chips does not resolve the problem.  My thanks in advance for any advice you can offer.

For those who are curious, the original artwork is still present on the side, although it could be in much better condition.  Whenever I don't have a billion things that need my attention, I'd like to take the time to restore the cabinet to its original beauty - if at all possible.  Haha...being a responsible adult sucks sometimes.  Who knows when this might happen.