Half of DOCK icons have disappeared
When I logged on this morning, half of my icons in the doc are missing. The programs are still there and working. I can hover over the space where they used to be and they are still there and working. The icons images simply are gone (and all I see is the grey of the dock underneath it). I tried restarting and shutting down, but they are still gone (and now a few new ones are gone).
I have not installed anything new and I have the latest operating system (10.11.6 (15G20015)). I have MacBook Pro (Retina, 13-inch, Late 2012) with 2.5 GHz Intel Core i5 processor and 8 GB 1600 MHz DDR3 memory. I know it is on the old side (bought in 2015), but everything works still... except this new little glitch.
Any ideas??
MacBook Pro (Retina, 13-inch, Late 2012), OS X El Capitan (10.11.6), null