Digital zoom has stopped working

I now have 3 Powershot TX1's that have developed the same problem which is, the Digital zoom not working. Everything thing else works fine. None of the cameras have been dropped or misused.

I know it might seem a little sad that I wont change cameras but i love this machine and have got some wonderful shots with it.. incidentally the  Canon support site doesn't even show it has the machine which seems a bit ominous.
If anybody can help Id be really grateful.
Thanks
Phil