Here's some LED codes from a manual. If this thing is pretty new, you probably won't find a schematic. IDK what voltages the 240W bulb uses, but there's probably not very many voltage rails to check, if it's already running.
From the pic's I'd guess there's a boost stage like to 340V maybe, and then another stage or 2 for driving the lamp.
And the little transformer on the far left might be for 5V standby, or 5/12V for all the circuits outside the PSU. If I had this to work on, I'd make my own schematic in LTSpice, but yeah it takes time.
I'd look up all those chips on the PSU, see if they have Vcc, and if any of them have an ENABLE pin, or a power-good pin. Pretty much all those controller chips will be checking for under-voltage/over-voltge, over-current, and might be shutting down.
There could be some power problem on the other boards, you can check for shorts on some other boards. And there could be a logic signal coming back to the PSU saying to not drive the light.
If I knew the low voltage rails to the rest of the machine, I'd even try powering that from some modem or cablebox PSU, or benchPSU if you have one, just to measure the current draw.
https://global-download.acer.com/GDFiles/Document/User%20Manual/User%20Manual_Acer_1.0_A_A.pdf?acerid=636595271962374228