PS2 turning on problems

[koalabear]

I have a PAL PS2 with a NEO4 modchip installed. Im having a problem where the PS2 turns on, but nothing comes up on the TV screen. All the cabling at the back of the tv is correct, as ive connected it up many many times. I pulled the lid off the PS2 and noticed there was a hole in the ribbon cable to the switch. I stripped the wire back, and the PS2 worked for about 5 mins, but has since died again. Ive even modified the same cable from the PS1, but no luck. Both the green and blue leds on the switch turn on and im able to open up the disc tray. Would anybody have any ideas where I should go next. I wanted to erase all possabilities before i started looking at all the wiring of the modchip from the main board. Thanks for your help.