Check your disk mate. Usually its either the disk or the Console itself. If the disk is clean and not scratched you should either take apart your PS2 yourself, and void the warranty or go buy a new PS2. The old ones get dirty and break down, like my PS2 is almost to the garbage and same with my old Xbox.
Just check for scratches or dirt/dust on the disk and try cleaning it with a dish soap or something and use a lint free towel to wipe off the disk so it wont get scratched or anything.
Avy & Sig credits go to Hurricane0