lost seriel number?

Hi, I’m using an old version of cubase - 5.1 bought already installed by Carillon who are no longer in business, due to a fault I’ve just uninstalled cubase, now when trying to re install I no longer have the serial number required for set up or the user name I used. Is there anything I can do or is that the end of it?
Thanks for any help,

Try contacting info-at-Steinberg-dot-de

Thanks I’ll give it a go.