Your Blu-ray laser may have gone out. Try the Disc Loading Problems page ( http://playstation.custhelp.com/cgi-bin/playstation.cfg/php/enduser/std_adp.php?p_faqid=263&p_sid=W8ly5NAj ).
If this doesn't fix your PS3, you will need to send it into Sony to get the Blu-ray laser fixed...