Basics would be, and you have done it as mentioned, are:-
Check how many satellites you are picking up, bottom right hand corner of the screen. This should be minimum of 3 ( triangulation from what I understand)
Pull unit out as you have stated, press reboot.
Connect unit to computer and check version upgrade (not referring to map upgrade, but the software itself)
Failing that, then if you know someone with Becker to see if their unit works in your car ( or vice versa). This to see if it's the unit or not.
I hope this helps and kind of banking on that a software version update may help.