So some questions to ask:
1) what was the psu you used?
2) how was the room it was in? by that was it really hot or really cold? above 90 f or below 35 f ?
1- DPS-1200FB-1 A
2- Chilly attic about 19c
It surely died when powered on - not from heat.
They want whole unit? seems a bit much.. won't let you just send the one board?
Yes, you do need to send the whole machine. The boards work together and they cannot repair one board without the other.