hopefully it's something I believe to be very simple...
if the board appears to be really dirty use the steps below:
I would just reseat the roms. use a small flathead screwdriver, insert on one side, give it a slight twist, then switch to the other side of the rom... gradually alternate between both sides until the rom comes out, you want to pull it as straight upward as possible so you don't bend the chip legs.
inspect the legs of each chip, and the sockets too. if there's crud in the sockets, you don't want to put the rom back in. you could just blow on those, or if you have a can of compressed air (and know how to use it properly without freezing things and not shaking them!) you can use that too.
if the chip legs have corrosion on them, gently rub some sandpaper on them to scrape the corrosion off until the legs are shiny silver.
then... reinsert, making sure all the legs are properly in the holes before pressing them back in with your thumbs.
if your board appears pretty clean:
on the flipside, none of what I just mentioned may be the problem at all, it could just be "chip creep", which means the roms actually slip out of the socket due to the cycling of power on the board, that you can just press them back down with your thumbs.
hope this helps and it's not a board/RAM issue!