Opus ITX not powering on motherboard

I have had the standard Opus ITX (powered by Opus 120 I think) package running for over 5 years now, and all of the sudden my motherboard is not powering on. Fans power on, but not the motherboard or monitor. Funny thing is, as soon as ignition is turned off, the motherboard begins to boot up, only to shut down once the shutdown delay kicks in. Any ideas on what the problem could be?

Looks like a jumper controlling startup voltages may have fallen off of the back panel. Should be fixed now. Carry on!

Ok so that didn't actually fix the problem. I can get it to boot now if I switch on power and ignition at the same time. But if power is already connected and then ignition is turned on... nothing. So weird.