Has anyone come across the problem that the radio controls no longer work except those on the steering column? I can't use any controls on the radio facia. It seems to need a reset - is there a button combination to do this - or just remove the fuse?
Firstly, as noel says, make sure you have got the code before you do anything.
By what you have said above, I take it that the headunit works ok with the steering remote still, nothing changed there?
Quite weird if it does. I haven't noticed on mine but I know on some HU's you can lock the buttons with the press/hold of one so they can't be altered. Have you got the manual for it? Have a look through and see if it mentions anything about locking or disabling the buttons in anyway.
If that doesn't work then try resetting it by disconnecting it from the power for a bit. You can either dissconnect the battery or just remove the hu which is easy on a Megane.
Whilst that is out look for a reset button around it. Might only be a pin size like on some things. If it has one of those then maybe doing it that way could help, however, I don't know what effect, if any, doing that will have on the code. I don't think it will have any effect, I know unplugging it won't.
When you plug it all back in, if it works and you are not sure how to put the code in then ask and I will talk you through it if I can remember, lol.