Did you just update to 38.3. If so, this will probably fix your problem.

1. On the toolbar then 
2. Select extensions and remove the Lightning (calendar) addon
3. Restart Thunderbird
4. Reinstall Lightning/calendar addon - if you need the functionality

Please tell us, does that help?

Note

1. If you can't get to Add-ons, then start Thunderbird in safe mode by holding the shift key while starting Thunderbird.
2. If you still can't get to Add-ons, simply reinstall Thunderbird from http://getthunderbird.com/

ncrooner said

Despite clicking on "inbox" or "reply" or anything for that matter.. the screen wants to remain on the main acct screen and prevents me from doing anything. If I right click on "open in new tab" i can get to my in box or even the individual message but still cannot reply or forward. It is as though I have lost my basic functions in a buggy way like a virus tends to do.

I actually reinstalled save version of thunderbird without lightning and it fixed everything. The program told me that Lightning was not a compatible addon so I left it off and it works beautiful. fortunately I do not need it's functions.

ncrooner said

ncrooner said

Despite clicking on "inbox" or "reply" or anything for that matter.. the screen wants to remain on the main acct screen and prevents me from doing anything. If I right click on "open in new tab" i can get to my in box or even the individual message but still cannot reply or forward. It is as though I have lost my basic functions in a buggy way like a virus tends to do.

meant to say I installed "same" version.. not "save" version.... sorry

I actually reinstalled save version of thunderbird without lightning and it fixed everything. The program told me that Lightning was not a compatible addon so I left it off and it works beautiful. fortunately I do not need it's functions.