hello, i have been having issues with my computer and had to send it away to get replaced. When i got the new computer and installed Crysis 2 i went to play multiplayer and had to enter my serial code. When i entered the serial code and my account name and PW it said the serial code was invalid. Is this because i had it installed on my other computer and can it be fixed.

One copy per computer, so if you have used that copy on another computer, you'll have to leave it on there. Some games do have a de-authorise option so you can use it on another machine.

the computer was taken bak by the company and i recived another computer

I was able to install it on my main PC and laptop without issue, maybe try contacting EA support