Power should be fine, the motherboard only uses a 24pin and 8pin for the CPU, the GFX card uses two 6 pin power conections.

I removed the card and ram cleaned up all slots as you suggested, same thing. I have now lowered my desktop res to 1280x720 and despite the fact i hate this res as everything is too big, i can atleast launch games.

Only thing i can do is switch the res before i start a game then back again after i finish. I not sure if this is mean the problems is solved or just a workaround. I can't see why my computer fails to start though after trying to launch a game from the higher resolution. The mobo book report continuous long beeps as 'graphics card not inserted properly' which puzzles me as when i drain all the power from the system and try to start again the card magically is inserted properly and begins to boot.

On the plus side i got too play BBC:2 for an hour today and on max graphics my temperature only went up 4*C in an hour.This was one thing that worried me about my custom case build, slightly off topic i know sorry .

I think i will continue too look into this though because i need to understand why it's happening. Thanks again for your help.

The graphics card error of not being inserted properly is very strange indeed and could be a major problem that only a replacement will fix. This could however be separate to your "unsupported mode" issue.

Typically the refresh rate of TVs are lower but since your running a HD card on it I'm guessing this TV supports a wide range of frequencies to incorporate the most adequate horizontal and vertical scan rate for higher scan rates without tearing. So the absolute first step is to check the frequency of the monitor vs the games, forcing V-sync on the graphics card will also help along with triple buffering.

Next we have DX extensions, if your worried about using newer direct x games with older versions simply change the extensions in the graphics utility program.

"My desktop screen resolution 1920x1080 @60Hz it also changes to 4:3 (from 16:9)"

What game, does the game support the HD resolution?
For aspect ratio try 8:5/16:10 instead if it's causing problems otherwise 16:9 is the standard. As a note though desktop resolution and aspect ratio will change to that of a full screen program, which is why the both should always match.

Honestly I don't know what to say other than to check your supported scan ratios, usually this would be "Frequency out of Range" but "unsupported" may be the error for that particular manufacturer.