There is a problem with the disc reader, you should try using a disc cleaner (easily found at places that sell the console), if this does not help, you will need to contact Sony about the problem and see what their tech support can do. Its a hardware issue and not easily fixed and should be fixed by professionals.
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THATS BECAUSE YOU BOUGHT AN XBOX 360!!
There is a problem with the disc reader, you should try using a disc cleaner (easily found at places that sell the console), if this does not help, you will need to contact Sony about the problem and see what their tech support can do. Its a hardware issue and not easily fixed and should be fixed by professionals.