Hi and welcome to Beoworld! Looking at the remote control problem first, the Beocenter may be in A.OPT 0, where is will not respond to remote signals.  To fix this, first power up the BC9500 as you have until the CODE display disappears, then with the Beocenter back in stand-by, use the BL1000 remote to press 'SOUND' then '1' then 'STORE'.  Then try the remote again. With regard to the CODE display problem, this probably means that the microprocessor's 3V lithium battery needs replacing.  The normal technique to  get rid of the CODE display is:

• Fix the battery or RAM and then
• Using a Beolink 1000 press:  1271
• After 3 seconds, disconnect the 9500 from the mains and then reconnect.  This should solve the problem.

If you wish to replace the battery, here's a picture of the location (red arrow).  You need to be careful desoldering/resoldering lithium batteries - not too much heat and wear eye protection just  in case. Login to view image And this is the replacement battery that I have used successfully in the past:  

Two things to add:

• You said you had bought a '100 remote control' - I assumed that you meant BeoLink 1000 remote (or BL1000) so please correct me if the remote is different!
• Do you have a service manual?  It would be very useful and is available on this site to Silver/Gold members.