iMac/TV connection issues

My power went out earlier (which happens a lot as I am on a payg meter) and when everything came back on my TV would no longer display my iMac screen. Both devices knew they were connected as when I unplugged the HDMI cable the TV said 'No Cable' and when connected again the iMac flickered and the TV changed to 'No Signal'.

I plugged the HDMI cable into one of the other ports on the TV and the picture came back on. I set the screen resolution and everything seemed fine again until I tried to unselect 'Mirror Displays'. When the screens are mirrored the TV picture works fine but the sound comes out of the iMac which isn't what I want, when I try to de-select mirror displays I am no longer able to change the resolution of the picture on the TV screen and it is unviewable.

I've been at this for three solid hours now and any ideas would truly grateful. Thanks.

 

EXTRA: I have a late 2009 iMac, and the TV is a Samsung UE32F5000. Before I got this TV I connected to my old one with a VGA cable and a male/male headphone jack, I gave the headphone jack a try but I got no sound from either device that time.