It's a VERY common problem on these version PS2s. It's known as the 'V9 Syndrome' try google - and its an instance where the LA6508 chip which controls the DVD Drive and laser mechanisms blows on the motherboard. It runs from 12v (which causes lethal voltage swings when the consoles' laser is weak and / or poorly copied / scratched media is used in the PS2). More likely than not, it blows the laser at the same time as the chip.
To repair it, you need to replace the LA6508 chip and more than likely replace the laser too. If this is the same laser from the time it last blew, definately replace it this time around (if you intend to fix it, that is).
You can stop it happening. You will need to replace that LA6508 chip to get it working again, but this time, when you replace it, do not solder Pin 17 to the board. Instead, solder a wire from this pin, and solder the other end to a 5v supply - which stops the problem. Just make sure you replace that laser before you power it back up however...
An example. and instructions on the Romeo mod can be found here:
http://www.cyber-mag.com/station/laserPS2.htm
In fact, here is a real good explanation of what the V9 Syndrome is:
http://www.cyber-mag.com/station/laserV9.htm
Good luck mate