Hi and welcome to Beoworld!  (BTW  I just responded to your separate PM) Are you sure that the glass panel is not loose?  It can come unstuck from its plastic surrounds over time hence does not make contact with the sensors below.  If so, it will need removing and re-gluing.  I have done this process on a BC9500 but not a BM4500, so perhaps others can help if there is anything specific to look for.  I have read that the sensors underneath the glass panel can also become mis-aligned, so you do have to be careful when re-fitting the glass panel. You'll get some ideas from this thread or a further search on the archived forums: 

Location: Warwickshire, UK

My B&O Icons:

BeoCenter-9500.png

Beoremote-Beo4.png

Beovision-10.png

Beotime.png

Beosound.png

Beosound-Explore.png

Beosound-Essence.png

Beoplay-P2.png

Beoplay-M3.png

Beoplay-H4.png

Beoplay-H3.png

Beoplay-Form-2i.png

Beoplay-Earset.png

Beoplay-A2.png

A very helpful reply. In fact my glass panel is detached. Since the Beomaster is sitting horizontally on a table I didn't thought it would critical to have the panel glued back again. Strangely most keys work so I will check the alignments of all sensors. Thanks Guy!