I have a 21.5 inch iMac and have it hooked up to a Samsung LED 40inch tv. its been connected and forking perfectly for some time now. but i had to disconnect the mac for a day and now that i have gone to re connect it, the tv shows 'mode not supported' The resolution is not supported on this TV. Please change the resolution. the TV is a full Hd 1080p one and so is my mac settings set to 1080p and 60hz to match the tv, but its not working anymore! any ideas on how i can get past this problem? or is it a fault with the mac/TV??