Try View then Layout and make sure the contacts box is ticked.
If this doesnt work you can add contacts to the toolbar by view , layout, customise toolbar and then highlight contacts and then click add then apply at the bottom of the box.
Silly question but could it be that the contacts box has been dragged down so that the line is sitting on top of the base line on the bottom left corner, try putting the cursor over it and see if it gives you the symbol (double arrow) and if it does try to drag it up.