Combo Box in Access

I give up on this, just doesn’t want to work. Form based on a basic table, I select all the fields to show up, than want to repalce the first field with a combo box, so that I can quickly jump to the desired record. I have a database MADE BY ME !!! that does the same thing, I can’t see a difference and I also don’t remember how I did it in the first place, although I think it was a pretty straight forward thing.
Thing is : it’s not working. I either scroll the combo box, but the other fields in the form do not refresh accordingly, or I get an error message when trying to select the first field (in the box), something about file not accessible, network connection might be lost (not the case).
I tried with a different database and the same things happens, I’m sure I’m missing something just don’t know what…