Sudden extreme slowdown of my iMac

My iMac has been working rock solidly for multiple years and as of a few hours ago has been running extremely slowly. We’re talking 3 minutes per click slow. So slow that rebooting it is a 20+ minute process, when it only took 30 seconds yesterday.

Any idea I can try to do to remedy this and what steps http://movieseriesworld.com/ I can take to prevent myself from losing everything if this is my computer turning into a brick? It’s been far far too long since I last backed up all of my work, but it’s certainly in no state to http://www.movieseriesworld.com/forums/index.php be doing a massive backup if I can’t even get it to load finder.

Edit: Also worth noting, most of the app icons along the bottom bar are also showing different icons from what the apps actually are. It just shows the icons for finder, trash, and activity monitor over and over again but if I hover over an icon it say last the correct name of the app, (photoshop, logic, etc)

Edit 2: Tried to reset PRAM and now it’s frozen on the boot up screen