MSI z77a gd65 unable to boot into bios

Here are my specs,
core i7 3770k
12GB RAM on 3x 4GB ram sticks
256GB SSD
Nvidia GTX 1060 3GB
msi z77a gd65
A PSU that is capable of powering it all

I was nicehash mining for a few days on gpu OC and I found my PC one day suspiciously off when I hadn't turned it off. I turn it back on and for a few boots it BSOD'ed after I'd typed my password to login, showing a different system error message every time. On one of those boots, it successfully logged in but I find that the performance is waaaay down/off. in what way?
1) Running 2 applications would just turn my cpu usage from it's idling 1 to 2% to like 30% or so. running 3 applications took it to 60% and at 4, we hit 95%
2)When I fast forward video playback by selecting a time on the time bar, the video halts playing and the CPU usage shoots to 100% for like 10 seconds and only then does the video start playing, after which CPU usage pops back to the 25% it was prior to the shoot(which is unusual in itself for my setup). This happens no matter where I place the video file(on my SSD, HDD a, USB stick etc) so I don't think it's a read issue.

On the last of those boots, I did a windows reset and reinstall and then it didn't BSOD ever after that. But the performance issues persisted without change. Same high CPU usage for ordinary tasks.

Some of the bits and ends were misbehaving.

1)When I plug my LAN cable into the wifi router, no internet, when I plug into the wall ethernet output internet worked fine. To be fair, this could be a router issue too.

2)The onboard HDMI out wasn't outputting even when the GPU was unplugged. To be fair, I didnt try the onboard VGA out.

So I decided to do some hardware fault diagnosis by elimination. Long story short, during one fault diagnosis reboot I switched to BIOS B. But instead of going to another BIOS, on the monitor it showed "Flashing bios A from external source, progress 0%, do not restart" I knew I didn't have another bios flashable connected in any of the USB slots(or anywhere else for that matter). On the very next line it said, " Progress 100%, restart" or something to that end. The only explanation that makes sense to me is that it had overwritten Bios A with garbage data, reading from a garbage source.

Now BIOS A doesn't boot. It tries to boot, CPU fans spin for a second and then stop, and then all the lights flash again as it tries to boot again, CPU fans spin and then stops. This is what keeps happening cyclically. As for BIOS B, its doing the same thing. fans spin then bust, fans spin and then bust.

What can I do to confirm my "the BIOS is garbage" suspicion?

If my suspicions are true, what can I do to flash the BIOS available on the msi website onto the on-board BIOS chip.

I am an electronics engineering student, I don't mind a technical guide, I don't mind breadboarding my setup. But I don't know how to do all that, I need a guide to that, if you could provide a source for that, that'd be very helpful.

I'm hesitant to buy a new motherboard cause I don't know what the cause of my initial performance issues were, (whether my CPU/RAM/GPU/all were wonky) and also if something was wrong with the bits and ends. So, buying a new motherboard for possibly faulty components is not something I'll consider unless it is my very last option. How can I get my motherboard to boot into BIOS again?