connecting macbook to HD tv

[minerva Andino]

i had my macbook hooked up to my (AOC Brand) HD tv, all was well and then i had to disconnect to move some stuff, when i tried to plug-in the HMDI wire to the computer, i get a "not supported" floating on the tv screen.
some one please help

i can connect mom's mac to my tv and all works as it should
if i connect my mac to another tv , it works fine
last night my mac was all a-ok on my tv...
but now, like i stated...when i plug in i get a "not supported" float...
any ideas????