DVI to HDMI on Plasma LG gives "Invalid Format"

Hi, this question is really driving me mad.
I've tried reading about it, and making several adjustments, but none have worked so far.

This is the problem:
I have a macbookPro (original) and was running Leopard latest version. I've just recently bought a TV Plasma LG42PQ1100, which has one HDMI port. The right assumption would be that just connecting the cables (DVI to HDMI) the TV would receive the sign, but when changing to HDMI input on the TV it keeps showing the message "Invalid Format". My mac recognizes the TV,as in the preferences it shows the display settings for the Plasma.

As I've been reading about HDMI problems in the forums, I've tried everything.
- SwitchResX to change the resolutions, and always the same case.
- Tried with another old Powerbook, since I had read that versions under 10.5.5 would work better with HDMI, and had the same result "Invalid Format".
- Tried updating from Leopard to Snow Leopard on my macbookPro, in order to have those display preferences to the new TV settings, and also... "Invalid Format".

The worst in this, is that I've tried these two macs on other TVs, and it worked straight away. Just plug'n'play.
Also, my Plasma is working fine before you ask, since trying to connect a portable Compaq via HDMI-HDMI also worked just fine.

What the **** can I do about this? Any other thoughts I haven't read about it in forums?
By the way, besides HDMI,I only have Scart input on the TV. Any other way I can connect via my macbookPro, as an option to HDMI?
Help appreciated....