PC froze, now won't POST

Four year old PC, Gigabyte AORUS Z390 PRO, i9-9900k, 4080 gpu, 32gb corsair RAM (less than a year old).

Was watching a video and both screens froze entirely, no BSOD but complete freeze. Restarted PC, power comes on to components/fans/LED but dosn't even POST.

Tried changing CMOS battery (and waiting 10 mins to drain it) Tried different RAM sticks in different ports . Tried taking GPU out and using onboard, using different screens etc. Tried unplugging all peripherals etc. Tried booting from USB etc (Just havent tried unmounting the m.2 nvme that has windows yet as it's fiddly cus of the heatsink)

No case/piezo speaker so can't tell if it's giving me an error beep.

Any ideas other ideas? It's had no prior instability before this (Except a dead RAM stick about a year ago, i replaced both etc) Also no magic blue smoke release.