Server 2012 RDS SSL - CRT to PFX Issue

Hi,

I've got a server 2012 environment, and despite the fact i previously managed to get RDS secured all perfectly, it's come to renew the certificate and i've got stuck.

I have installed the CA and the SSL in the right places, but i can not export the certificate to a PFX file with the private key, i cant find the private key either, so i'm stuck and for the life of me i can not remember how to proceed!

I need this PFX file to then install in the RDS Manager