I think this is the third time posting this, but this should work.
http://www.geocities.com/djyayo/PS2errorFAQ.txtSeeing that you can only play DVD games, and not the CD games, it shows that the main reason for the problem is not a dirty lens. There\'s only one lens in the ps2, and if one type of media can be read, and another can\'t then the root of the problem is not a dirty lens. Of course cleaning the lens can and probably will help a lot, ultimately, it won\'t solve the problem and the problem will be back again.
The main problem that you\'re having is caused by improper voltage going to the laser that reads the CD-rom format. With time, electronic devices tend to deviate from what they were originally set at. Voltages drop, resistors stop working as they used to, etc etc.
The manual that I linked to shows ways to adjust the voltage. But be warned, do it only if your warranty has worn out, and if you have confidence in what you are doing. If not, I\'d suggest either doing the swap trick as someone else pointed (although supposedly its illegal) or sending it to sony and paying them some lump amount of money (which i wouldnt do, cuz it\'d just piss me off to have to send them more money for something they should\'ve thought of in the first place)