On board computer problem

I have a 2000 bmw 328 Ci which i bought used a few months ago. The car is equipped with a navagational system and a onboard computer. the
navigational system works fine, however i can not get into my onboard computer options. On the screen there are different options that you can click on. They are: On-board computer, set, navigational system, emergency, and monitor off. In order to select each one they have to be like bolded in white. So therefore i am able to select navigational system, emergency, and monitor off. But iam not at all able to select set or onboard computer options so i can never set the date or an other options that come with the onboard computer. It is funny however because sometimes like it will start working and let me click on the onbard computer and set selection but as soon as i get in it kicks me off and puts me back to the original screen. i am asking if anyone may know what is wrong and if its just something simple or something because the dealer wants to charge me 90 dollars just to look at it. i would really appreciate any help. Thank you very much.
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