Lightroom 5 - images never finish "loading" (cannot develop)

Hello, I'm hoping someone can help me out.

I'm running LR5 on an iMac. It's been working fine for the last year or so but about a week ago, while the program would (sometimes) start and I can select images but they never finish "loading" and therefor I cannot develop them. (This also happens under the library tab.) In the past, when I would select an image, it would take a half a second to "load" and would then become sharper and the develop controls would go from greyed out to usable. Now, a little black bar which says "loading" and a spinning wheel just keeps going, never actually loads, and the develop controls never light up to use.

I've tried un-istalling / re-installing the program with no success. I've contact Adobe which told me to ask here since they are no longer trained to help with LR5.

A few other things which may help troubleshoot:

-I am able to see the thumbnails of my images and when clicked, they do change the picture in the main view window.

-The program opens unreliably - in order to open it the last time I had to shut down my computer and restart.

-It seems that, sometimes, even when I "force close" the program it remains open in the background and will not restart (i.e. will not open again in a window).

-I've tried deleting the .lrcat.lock file after force closing (as described in another page of this forum with no luck).

-My mac was updated yesterday to the newest operating system (i.e. this problem began prior to that update).

Any help would be greatly appreciated - this is very frustrating.

Thank you,

Alex