the "big" ps2 have a 90 day warranty, check the docs that came with it.
To start, with unplug the unit remove everything you have attached to it, memcards, controller, NIC etc..
grab a couple games, plug it in, and turn it on. see if it boots, try with a few games.
if it doesn't work and it's still under warranty take it back for another.
not under warranty, then try a cd laser cleaner on it.