cdr500 problem?

Hi, I have a corsa b and I changed the radio for a cdr500 cd player everything has been working fine til the battery went flat. i have the code for the cd player but when i turn the engine on and turn it on and hold the as button nothing happens. I have checked the fuse but the dash is still on. It only shows the date and time etc. Its like there is no power going to the cd player as the led red security light has stopped working . Can someone help me please. thanks