This may be a long post but I wanna give as much info as I can.

So I recently embarked on my first PC build. It was a long process with a couple of RMA's and various teething issues but last week, finally, I got it working. Spent the past week getting everything installed (games, programmes, settings etc). Ran fine for a week, no issues at all and then suddenly last night the screen goes black after ending a gameplay recording (elgato software) and the Q Code 8 on the board (8, not 08). In addition to that the button on the case won't power the system down (but it will power it on) and both the KB and Mouse are not lit up as they should (confirmed as working on another PC).

I've read through lots of forum posts and tried lots of trouble shooting including clearing the CMOS, flashing the bios to the latest version via the bios USB port (3502 when fault occurred, now on 6101). I've taken the ram sticks out and re-seated them, tried alternating them numerous different ways and still nothing. It'll turn on, everything inside the case lights up and looks to be working but no picture at all. Everything is at it's stock settings, no overclock at all on anything. Even the q code isn't mentioned in the manual so I'm at a complete loss as to what's happened, why and how to fix it. Any help is appreciated and the specs for the system are below, thanks in advance.

Specs:
Ryzen 1700x
Kraken X62 AIO
Crosshair VI Hero (non WiFi)
G.Skill Trident Z RGB (16gb @3200MHz)
MSI Lightning X 1080ti
Seasonic Focus Gold 850w