Unforunately this is a common problem on the PS3 and is caused by a faulty blue-ray drive. The unit will have to go back to Sony for service.
You could try a DVD cleaning disk first to be sure that dirt on the laser lense is not causing the issue.
You can also open the case and clean the laser lense with a Q Tip and an alcohol cleaning solution.
If you plan on opening the case at any stage please ensure the unit is disconnected from its power supply.
If this fails and you are confident with electronics there are several videos on YouTube showing how to replace the drive if you choose to order it and do it yourself.
Otherwise I believe Sony are doing these on an exchange basis for around $150 if your unit is out of warranty. You can contact Sony customer support at this link if you need to do this.
my ps3 will let me load a game but if i sign in to net it just comes up with a blank screen then...
(More)
my ps3 will let me load a game but if i sign in to net it just comes up with a blank screen then freezes
my ps3 power comes on, the blue and green lights are on, it's all connected properly but the...
(More)
my ps3 power comes on, the blue and green lights are on, it's all connected properly but the wireless controller won't find it and nothing appears on screen ?