How do I get my ps3 to play blue-ray movies?

[Blackwolf]

I recently bought a ps3 console and have had no trouble playing games on it. The other day I decided to rent a Blu-ray movie to see if it will play and it gives me the message: 'Playback of this disc using the connected device is prohibited.'
Are they talking about the cables? I don't have an HDMI connection on my tv, so I had to use the AV cable it came with. Is that the problem, or is it something else? Can I just not play Blu-ray discs with that cable?
If there are some settings that I have to change, walk me through it as I'm still new to the ps3. Also, I'm not connected to the internet with it, so no Ethernet cable is on there. Does that matter?
Thanks for any help.
There was no troubleshoot answers in my manual. Just a list of what types of discs it plays. And some people are saying you don't need an HDMI cable to play Blu-ray. I have a 250 gb ps3 by the way, and an old Sanyo hdTV (even though it has no HDMI hook up)
I tried a regular dvd in it and it plays fine, as do my ps3 games. On that note, can someone explain why the ps3 Blu-ray disc plays and not the movie ones?
Thanks again!

[AVDADDY]

All of your answers are in the manual.

[828]

Yes, they are talking about the cables.
Whether you're using a PS3 for Blu Rays or a regular Blu Ray player, an HDMI connection is required. The Blu Ray audio and video is carried through the HDMI cable. If you do not have that cable connected to an HDMI compatible screen then it simply won't work.

The ethernet cable has nothing to do with it.

[The Shadow™ ®]

blu-ray requires the use of an hdmi cable or component cable with the console set to use HD resolution
if you do not have an hdtv then try a component cable and see if that can fool it into playing the blu-ray
blu-ray content is hd so does not play on older SDTVs or would play with very bad resolution and possibly no color