could be your laser is going down the pan slowly or has a dirty lens.
have you tried cleaning the laser lens.....also are your games clean ?
make sure the front vents under the front of the PS2 are not clogged with fluff.
cheers,
Daz.
PS my laser packed up after 3 months old..cos i chipped it couldnt claim on warranty so bought a replacement laser for £27 from
WWW.LIK-SANG.COM fairly easy to fit too. works a treat again.