CS4 Serial Number coming up invalid after years of use

I purchased the CS4 Master Collection some time ago, I know it is really out dated, but it works for me , now I am being prompted to enter my serial number when opening the programs (which worked yesterday???). When I put in my PAID for number I'm getting a red 'X' instead of a green check mark. How can I resolve this? The suite has been on my new PC for over 2 years with no problems until now.