OK, so this indicates the buttons are bad. While "programming" on a button shouldn't be lost, the fact that the buttons don't work for another device indicates to me that the physical buttons are bad. The button fix I posted about above should fix that.

NOTE:  When you tried the code #'s that Brad posted, did you try buttons other than Menu and the #3 with each code?  

So your MX-500 is 20 years old too! They were built like tanks. I've been using my 850 daily for over 15 years and it is rock solid too.

If this happened to me and if the 500 with programming that you just ordered works, I would still get an MX850 and if necessary learn the Sunfire commands to it if they aren't already in the database. Then save that onto your PC. The software is a lot easier to program than doing it on the 500.

Let us know how it works out.

@Brad Would the firmware be different between the Sunfire remote and the 500 because the Sunfire remote would already be programmed and perhaps that program is part of the firmware? This would prevent a user from overwriting the buttons when trying to add a TV, DVD player, etc. Looking at the manufacturer code list posted here on Remote Central ([Link: remotecentral.com]), Sunfire isn't listed.  Wonder if the codes were added in a later version of the 500 database? Or it was simply left out of the list here.