I've had my 90 Accord for about 6 years now and it's been great, but suddenly the moonroof doesn't respond at all when I press the button to open it. I know if I take it to honda they'll charge big bucks just to diagnose it. Any suggestions from anyone on what to do? Is there anything I might be able to check out for myself?

have you check fuse for it?

Not sure where the fuse for the moonroof would be located, and don't have the manual that came with the car. Where would I find the moonroof fuse? If you know a site or anywhere I could find this, it would definitely help.

I never had 4gen Accord, but from experience with 3, 5 & 6 gen Accords i can tell this; there are two possible locations of fuse boxes.
one is under hood, it should have black plastic cover on it, on cover you will see fuse schedule, see if it says moonroof or sunroof fuse, if it is you need to pull it out and see if you can see link (Z-shape wire) between polls. if that link is missing you need to replace that fuse with same size (shape and amperage rating).

second possible location is inside of cabin; on driver side, some where below air vent. it also should have fuse schedule on it.