SGT Arc Angel7

So, I'm having this weird issue where my GPU usage goes from 100% down to 0% for a LONG time, then goes to 100% again. I am having the weirdest lag I've ever experienced, it just feels choppy and just off. My frames go from 144 to 10 within a second. My software is saying that my display is not FreeSync compatible which is weird. Everything else is fine. CPU usage, RAM, even VRAM is only at 77%. It's such an issue that I'm having to play Wasteland 3 on my Xbox instead, because it's lagging so hard it is causing glitches in game. I've never even heard of something like that before. This all started after my PC was having some weird posting issues and I had a computer shop fix it for me. The PC was fine for a day, now it's doing this. Please help me out, thank you guys I'm posting pics of the usage on Radeon.

I've had my PC for about 3 years, and never had an issue. Yesterday, I tried to boot it up, and my PC never even got to post. I tried booting a few more times and same thing. All lights were on, everything had power, but nothing was showing up on screen, and all USB devices were getting power but no data flow. Naturally, I unplugged everything and plugged it back in. Then it would turn on and get to post but it would freeze up everytime. Now however, it powers down randomly. The furthest I got was to the login screen and that's it. The longer I leave the PC off the longer it stays on. If I try to reboot it immediately after it shuts itself off it just shuts down again immediately. I'm really lost and not sure what to do. It's such a random outcome issue that I have no idea what the problem is. Windows 10 Home 64 MSI B350M motherboard Micro ATX 16 GB of 2200mhz ram Corsair Vengeance 2 sata SSD, a samsung 2tb and 500gb RX 480 6GB Raidmax Thunder 735w