[spooky]

Definately sounds like the laser to me.

if its like the PS1 and PSX then you could try re aligning it. on the laser assembly itself you sould find some small pot's that can be adjusted, maybe one on the ribbon similar to the PSX units. Give it a go as you have nothing to loose. just be careful when turning these pots, light finger presure is all thats required. just twist about 1/8th of a turn and try to re boot, if it seems to get worse then turn the pot back in the oposite direction, repeat the process. If all goes well then you should find a position where the laser will read quite happily for a while. this is not a longterm fix but will save a few quid on a new laser for a few months. (And theres nothing like buying something cheap off a mate, fixing it for no cost and then rubbing their nose in it.)