Ouch.
I empathize. My last round of upgrades went to shit and even now I'm stuck with a computer that has horrible performance issues when I run games. The game itself will usually be fine, but everything else is fucked with their memory usage going bonkers and usually having to force their closure.
I have no idea where the problem is with mine.
At least with yours you have a starting point: your motherboard. It's fucked. I'm not sure if it was fucked from the beginning, but it's definitely fucked now if you can't get into the BIOS. The driver problem is probably also related there, and like you said it might be the culprit for destroying your memory.
That *might* give you a measured response, depending on what slot/socket type your CPU is, and how many pins your memory has. If they're current enough then maybe you can just start with a new motherboard. But if they're not current, well... you might be back to the joy of getting a new motherboard, CPU, and memory at once.
I'd offer you a spare motherboard I have after last year's botched upgrades, but I'm not sure I'd even trust it. I sent it in RMA to the manufacturer and they returned it evidently working. If you think you might want that, though, let me know. It's just gathering dust right now. But it'll probably require you to upgrade your CPU/memory to a newer version. But if it looks like you need to upgrade everything anyway, well... maybe it'd save you $100+.
But I digress...
The most extreme thing you could do right now would be to reinstall Windows altogether. Maybe you'd get lucky and that'll get it working well enough for now. Plus you'd have to (or should) reinstall Windows anyway when you switch out your motherboard, so maybe that's a last resort strategy.