Not sure it will fix your problem, but it doesn't hurt to try.
1. Turn off/unplug PSU.
2. You want one of these, a jumper:
2b. You probably don't have one of those. You might need to use something like a screwdriver to touch the two pins (and nothing else) instead.
3. And you want to put it on the circled pins.
4. Wait 10 seconds or so, remove it.
And you're done, you can turn on the PSU and try booting.
You can also be glad messing with jumpers is mostly a relic of an earlier time, this is about the only time you ever see or use them these days. And higher end motherboards have buttons for this now.