Mini Displayport to HDMI not working with my PS3

So I got this adapter. Belkin - Mini DisplayPort-to-HDMI Adapter - F2CD021EB

And hooked it up to my 27in iMac, plugged in my PS3 (which I had already set to only output at 720p) and when I press command+f2 nothing happens. Do I need to get an adapter that is an actual converter box like the expensive kanex and belkin ones?

Just checked Kanex's site and they have this cable that looks promising. http://www.kanexlive.com/mdphd10ft

And ideas guys?

First off, you're not looking for a "mini displayport (or mdp) to HDMI".

What you want is to go from "HDMI to mdp.

Yes, there is a difference.

Second, whether it can even be done depends on which iMac you have. You need to verify your iMac is capable of video input. If it is, you're not getting away with one of those relatively cheap adapters. You're going to need one of these 3 adapters. They are the only ones out there that I'm aware of.

Belkin AV360™ Mini DisplayPort Converter for 27"iMac F2CD007
http://www.amazon.com/dp/B003LGOWNQ/?tag=macforums0e4-20
http://www.bhphotovideo.com/c/product/810604-REG/Atlona_AT_DP300_HDMI_to_Mini_DisplayPort.html

Those were just the top hits when I searched - could be better price somewhere. If you have a current model iMac - hang it up - not going to work.

Yeah, I realized everything you just said about 10 minutes after I posted. Luckily the Kanex HD is only around $100 on amazon. I'm sure (pretty sure anyway) my iMac works, it's a late 2009 27in model.

Yep, if you've got a model prior to thunderbolt, you should be good.