heres a wierd one for ya...

got a system hooked up to my telly via hdmi when it is connected i loose all win channels and prime goes to shit unplug the hdmi and all is good.

i am thinking maybe a bad earth is interfering but no idea

what have you tired so far?

Have u tried swapping out the cables? Might be a dodgy cable and is producing some sort of EMI that is screwing with the TV signals.

I find a similar thing when I attach via DVI.

Obviously a digital tv, pop open the info panel and check the signal strength. Perhaps if you put a inline booster you may recover them (as I did)

Also, is there anything like VCRs in line between the aerial and TV?

I did this about 10 times before twigging, when I was plugging in the xbox, I'd unplug the VCR, (same thing with the DVD-R too) and the signal strength would drop to a 1/4 of original. All devices need to be powered between or it suffers.

Most VCR/HDD/DVDR boxes also contain signal boosters.

nah its a direct connection to the telly.
i am thinking its the dvi cable(i am using a dvi to hdmi adapter)

sunds like a faulty power supply

id bump upto a corsair 1200w and maybe look at dual connecting power into the tele