I'm going to show three images of what you should see.
The above is what users who are not logged in see. You'll note the Log In/Register link in the Upper Right corner. You'll note I just added the same link in the Navbar, but I just dd that.
In the above, I've logged in and the link has been replaced with my User name and Avatar.
In this final image, there's a drop down box when I mouseover my Username.
I'm hoping that my adding a link to the Navbar cures the problem for most, but I'm also suggesting that if you can't see the regster link, you most likely have a very old browser and going to have problems on more that just this site.
I'm going to suggest trying another browser and/or update your browser to see if that helps. If it does help, please post what browser and version didn't work.
If updated doesn't work I'm guessing it is your antivirus or firewall.