Hello there
From what you have said it sounds like you have the Disk read error
The main causes are Hardware failure, overheating or wear & tear.
You may need to perform simple maintenance, clean or in some cases adjust settings.
To get the best advice on where to start I recommend a PS3 Repair guide,
http://www.ps3problemsgone.info From this you can fix the problem at home and avoid any large repair bills. Its easier than it sounds when you have help from the guide.
The other solution would be to send the console off to Sony, This is free if your still in warranty. If your console is out of warranty then the usual price of repair is $150
I am Glad I could help.
Best Regards
Petong18