I know you've probably checked this, but some DVD players have a key lock function that will disable all functions on the remote and the front panel. This can only be removed by clearing the key lock by the key lock button on the remote. I have an older off brand (cheap) DVD in my second system and it has this feature. It could also be that the Infra red pickup in the DVD player has died and is not recognising the I/R signal. If you have one of those "Universal" remotes you might try that on your player and see if it works.