The HDMI inputs are assignable so you need to make sure to assign the input selector you want to use to whichever HDMI port you plug the PS3 into. If for example, you want to use Cbl/Sat and you use HDMI input 1, you need to make sure Cbl/Sat is assigned to HDMI 1.
Some assignments are set by default so if you just press the various input selectors you'll find out which one is assigned to the HDMI input you used (of course the default settings are listed in the manual). This assumes that the PS3 is configured correctly to use HDMI.
There are other HDMI related settings as well. Particularly you need to set 'TV Audio' to Off so the receiver keeps the audio portion of the signal and sends it to the speakers and not the TV.
Onkyo manuals are usually very good but the receivers get more complex every year. I'd suggest reading through the HDMI setup and then come back and ask more questions if you still have trouble getting it to work.
