PS2 Not Working (Sometimes?)

OK guys this is my problem.
Got new laser unit for v3 PS2
Inserted it fine - worked no probs.
Suddenly not working - damn browser with circle of lights appear - took CD drive apart made sure ribbon cable still attached to laser etc put CD in & started to work again.
This has happened a few times since. I dont seem to do anything to the connection and then it works for a while (weeks) then stops again etc etc etc.
I dont seem to be able to get it working now tho'
Any ideas?
Should I return the whole thing to laser supplier or does anybody know what maybe wrong or how to fix this problem?
Cheers

Maybe the laser ribbon that you are messin with to get it to work is a bit knackered, try a new cable.

Last night I opened it up, checked solder points - all well, opened the CD drive unit, touched nothing & bingo! it works again.
I touched nothing but hey WTF it works!
Wierd.