Can't input radio codes. Why not??

Last weekend I took my 2001 Honda Odyssey to Advance Auto for a new battery. Before removing the old battery, the A.A. technician plugged a jump-start box into the 12 volt power plug inside the van to keep the radio codes from having to be reset when he disconnected the battery. When he was done, and I had a new battery, but the radio would not turn on so I could input my radio codes. The fuse is fine and the red security light blinks (so there is power to the unit), but the radio won't turn on and display the "coDe" message on the display so I can input my 5-digit code. I called the dealer and they want me to bring it in, but I'm hoping someone out there has had a similar experience and can save me some time and trouble. Thanks in advance.