I installed BIA on my other computer, which did not have the right specs to play the game. So now when i try to run it on my other computer (which does have the right spec) it wont let me activate my serial key. Do i have to buy the game again? or is their someway to play it on my other computer?

I don't see why you shouldn't be able to. After I played BIA:RTH30,I gave it to my brother. He was able to load it on his machine and play it. Then when BIA:EIB came out, we bought two copies so we could play multiplayer. I mean, if you need buy a new machine, you shouldn't have to replace all your software.

well, can i call support and get another serial key and i have proof of buying it ( which i bought online and downloaded).

Of course you can call them. Whether they give you another key is the question.
I'm assuming your talking about the installation key and not the online key.
You could try the installation key that's been posted on this forum in some other threads. I think it's generic, but I really don't know anything about it.