Try some of the common fixes for disc errors:

Clean your disc with a lint free cloth.

Try rotating your system -- as he PS2 seems to have an easier time reading discs when it's placed vertically due to the lens location.

Try running the PS2 in Diagnosis Mode. Load your PS2 without a disc inside and wait until you get to the main menu. Press Triangle and highlight "Console", then press Triangle again and set "Diagnosis" to ON. What does this setting do? It focuses the laser on the disc so that it has an easier time reading discs (this usually doesn't work, and I typically regard this as something Sony can just tell you to try over the phone).

Try a lens cleaning CD. These are relatively cheap and function with practically every electronic disc-based gadget. They have small imprinted bristles that clean your lens and disc space as the CD spins inside of your console.

Or try what Hannibal Lecter mentioned and use a compressed air vacuum to shoot any unwanted dust buildup out of your system.

All turning your console vertically does is give the console more stability and air flow space compared to placing it on its side. As long as the console is not in an enclosed space then air flow isn't a big concern, although having a better flow of air prevents overheating and dust from settling in. Because the PS2/PS2 Slim does not overheat easily, this suggestion is just more for preventing dust buildup and giving your console more space to air out and enables better heat dissipation.

The disks will spin and read fine, provided you don't bump the console while it's turned on (which you shouldn't do even if it's laying flat on it's side).

Okay, for some reason, my brothers' PS2 will scratch any disc you put in it... Got any ideas why?

my ps2, for some reason, doesn't Play any Cd format (cds, and games with "Blue Backs") games. Can some one help me?

in responce to Chimaira questionmy ps2 is an normal ps2.

Oh, and Thx for telling me this, Chimira:D

Hmm....... I wonder what's wrong with it.....