I've same problem. I have serial and activation code, but they don't work. When I insert them and press enter the program quits without any message. I use Win7 64x now and when I installed SSM it was XP 32 .. may be I need to reinstall again ?
Any changes in hardware will result in a NEW unique key being generated. This will be different from the key/serial that you got in the email with the original purchase.
As Christa has said, if you've not requested this before you can contact Exciting Similuations' support (from the email address that you purchased the sim from initially if possible), provide the new key the software is now displaying and they should send you a new code back which will work.
I've used this service and its quick and easy