PS2 Problem - Tray wont open, eject flashes

[reddragon105]

I've got a v7 PS2 (39003) thats modded with a DMS3 v2. It was modded about a month ago and has been working perfectly since then. However today a problem occured. The PS2 won't boot up at all, it powers on (standby) and comes out of standby with a press of either the reset or the eject button, however no picture comes on the screen, and if the eject button is pressed, it flashes on and off for a few seconds, then goes back to solid blue, without the tray opening at all.

I tried taking the console apart to have a look at the tray in case it was stuck, it seemed fine. I powered the console on while it was in pieces - and it worked! so i put it back together... and got the same problem again... seems a bit strange, i figured there must be a short somewhere.

i checked the mod install and everything seems fine, all good connections, nothing obvious.
i screwed the big metal plate back in place, tested it and it still worked. then added the hard drive chasis and tested again, still worked.
however when i added the bottom of the case - i got the original problem again.

took everything apart again, back to just the mobo and PSU, and it worked again. replaced the piece of metal, fine, replaced the hard drive chasis, broken again.

if its working with the big piece of metal on, what difference does adding the hard drive chasis or case make? as they dont touch the mobo itself they cant be causing a short...

one theory i came up with is that the PSU could be faulty and causing interference... is that a possibilty?

any ideas/suggestions?
________
Mercury Zephyr specifications