It is a disc reading error. Started to happen to my PS2 half a year ago. If you find a good guide it is hardly dangerous. I am the DIY type of person. All it takes is a bit of patience and a half hour of your time. Just make sure to be careful. The only instances when you run the PS2 while having it apart is when you adjust the lens, but you have the cover on the CD area, so you should not have a problem when you are testing it.

If it truly a disc read error, buying a new game will not fix it. Actually, at one point it got to the point where my PS2 no longer played any new games and only old ones. :/

Here's the guide I used! Hope it is useful. PS, you need a jeweller's screwdriver. You know, the itsy-bitsy ones?

Here

Read through it several times until you know what you have to do and are comfortable doing it. Also keep it near by in case of references.

EDIT: If you are not comfortable doing it then perhaps get someone you know to do it, especially if you know someone who regularly does this sort of thing.

EDIT2: BTW taking the PS2 apart invalidates the warranty. It is usually a year warranty for the PS2. So if it is still under warranty get it fixed professionally.