Hi, your PS3 might be trying to output to analog. Try doing this:
Turn off your PS3. Now press and HOLD the 'On' button on the PS3 itself (not on the controller). It will beep and reset the connection type. I believe it will use HDMI if available, if not then it'll switch to AV.
Also make sure the HDMI cable or AV cable your using is working. Maybe your TV/Monitor is set to the wrong input (which is unlikely but may happen, sometimes the fix is easy like that)
I hope this works for you.