Before you purchase a PS2 Repair Guide and take your machine apart, consider these options first:
1) Stand your PS2 vertically.
This is the way the PS2 is meant to be. My PS2 wouldn't play Blue game discs or DVD's until I did this & it works fine now. ( The PS2 logo on the tray rotates for display by the way!)
2) Phone Sony.
I called the Sony Helpline ( do a search for the number online - easy to find) and they said they would repair my PS2 for £50. ( See above - not needed in the end.) My PS2 is around 4 years old so the warranty has long expired. Sony may refuse repairs if your PS2 has been opened up.
3) Search the web.
If Option 1 doesn't work and Option 2 is too expensive, just search for online guides. Many forums will have free advice on how to repair your PS2, at the cost of a few minutes of searching the web.