FSX Deluxe Edition Activation

I've bought a new PC and I installed the FSX (Deluxe Edition), but when I try to activate it says that O have exceeded the number of times I can activate this product with this product key.

What can I do now?

Call them, there is no limit...you paid for it.

https://www.microsoft.com/en-us/licensing/existing-customer/activation-centers.aspx

Don't forget to add SP1 and SP2 unless you have The Acceleration Pack (it contains the two Patches).