Atec 42" PSU Fault

[sabre504]

Hi all this Atec 42” came in stuck in standby.
Shows red light on standby but when you press power button it goes green then goes orange
But the screen shows no sign of life at all .
Power supply is an IPLV-42
No 24v at the inverter plugs (not shorting to ground )
No 33v on psu to main board (not shorting to ground )
12v and 5v on the main to psu all shorting to ground
Q101 short not yet changed
The short appears to go all the way back to the schottky diodes for the 12v and 5v rails
Any ideas as to what could cause a complete short like this I don’t want to just change parts
and blow them
Thanks in advance