Formula displays in cell and does not work. Random issue

I need some help from the experts on two linking issues.
1) I am linking cells from one wookbook to another, I press = in the first cell navigate to the cell I want to link to in the other workbook, select it and press enter. This works most of the time, however on some random occasions the formula text appears in the cell.
2) In order to save time going back and forth between the workbooks I will copy the cell and paste it in the next cell, and chage the cell number/location in the formula bar. Again, this works most of the time but randomly the formula text appears in the cell.
What is going on here? is there a faster way to link multiple cell?
Any help would really turn my Saturday around.

Thanks