Check where you keep your PS3 while playing. Could it have overheated, if for example you keep it in a cupboard. If you think so, move it to a better place, then let it cool for a while. The PS3 has a great cooling system, it just ocassionly overheats in enclosed spaces.
This could only be a software fault in the PS3. Turn off the console completely, wait an hour or two and then try again. If it still doesn't work, try the following:
1. Don't open the console. If it only doesn't play Blu-ray discs (movies and games) then it might be the lens that reads blu-ray disce, which is a seperate lens from the CD or DVD reader. Call the Sony helpline (UK: 08705 99 88 77 national rate, as for US I am really not sure since I'm in the UK.) They will give you advice.
2. If you don't want to call Sony, most games' stores will find out what the problem is and fix it. Or, if you can, get the console replaced (though you will lose the data on your hard drive.)