It sounds like the capacitor on the flash board isn't charging. They're small electrolytics that go bad in time, but usually are good for a few years. There could also be other problems such as a cracked solder joint on the board. It could also be a fault with the main board, but not likely in this situation.
The unit will have to be serviced, or at least troublshot, and you might contact Moultrie to see what they can do, or what they offer for support. I couldn't find a site for them online, so refer to your manual that came with the unit.
As an alternative, you can run it by a local repair shop, and see what they would fix it for.
Always get an estimate first, since it can run a bit.
Good luck, and hope this helps.