DURABRAND CG5660-M is asking for a Lock Key Code. Help!?

I have a DURABRAND CG5660-M Digital Set Top Box. When all the connections are in place and I switch it on I am being prompted with a message saying, "Enter Lock Key". I have tried entering numerous sets of digits but to no success. I do know that it is a four digit code of numbers 0-9 but have no idea what it may be or how to find out as I have lost the manual. I have been searching the internet all night and still haven't been able to find any codes.
Your help would be appreciated!!
Thanks