Insert/Edit link and Remove Link buttons inactive

Hello,

At some point my insert/edit link and remove link buttons stopped working. I researched on the forum and have tried all of these to no avail:
1) Checking in both Firefox and Safari to make sure it wasn’t browser specific. I have the same problem in both.
2) Switching to 2015 theme and it had no impact.
3) Deactivating all of my plugins in both 2015 Theme and my current Retina theme, also with no change.

I am uncertain what to do next. Any insight that could be provided would be greatly appreciated.

thanks,
Lee