As the title says, won't let me do a thing to it. This is after I have been editing it for awhile. (Session drummer)
 
I closed and opened again, no dice...
 
The clip is not muted, I checked that already.

Is is Archived?

Is it possible the track view edit filter was switched from "clips" to "automation"?
 

+1 to <edit filter was switched from "clips" to "automation"?>
 
I think Biscuits may have the hit the gravy train on this one.
 

This seems to be an issue in the latest update. It happens randomly, and my workaround is to switch the edit filter from 'clips' to 'notes' then back to clips.

FWIW ... I installed 2017.04 today, and my PRV would not show all of my tracks, regardless of folder open / closed, archived, filters, etc.
 
Then I discovered this.  I use screensets to swap between views (TV, PRV, etc).  But NOW my screenset for PRV seems to lock in only the tracks selected the last time I used that screenset ... and so my PRV screenset is kind of useless.  PRV works OK if I select PRV from the menu, or use ALT 3, to open a fresh PRV.
 
I never had this problem prior to 2017.04, I am hoping my other 9 screenset views are not affected as well.  I use screensets extensively.
 
I just opened a separate post for this.
 
Jim
 
 

Biscuits
Is it possible the track view edit filter was switched from "clips" to "automation"?
 

How do I get there?? I have no idea where that is?

Simplest method - Shift+Click on the MIDI clip.    A Shift+Click gesture changes the Edit Filter to the object type you've clicked on, so you can also get back to automation by Shift+Clicking on it.   Or using Shift+Right-Click swaps between the last two types.
 
FWIW, the Edit Filter is also available in each track strip and by using the T shortcut key to open the Tools palette.