my ps2 stopped playing dvds once, a well placed hit fixed that problem (seriously), but i wouldnt suggest u do it.
instead get a lens cleaner and use it, also it would be wise to use a can of compressed air to clean the insides of the ps2.
if all this fails call up sony. but if yer planning to this, i hope you haven\'t opened up yer ps2 as it voids yer warranty also sony wont even touch yer system if u do it.