i've purchased LR 5 and some minutes ago i've subscribed PS+LR offer. I've installed PS CC and when i start PS it asks me serial number…
Same here! LR 5 is fine though. PS CC asks for serial or starts as a trial.
I have heard it can take some hours before it will get the message that you've subscribed.
Just use it as a Trial for now, and if by tomorrow it doesn't accept your Adobe ID login as enough, you'll need to call Adobe Customer Service on the telephone.
If issue persists, then Click the Chat Now button at the end of the page and talk with a live agent who would resolve it ASAP.