For starters, I've noticed that this problem only happens to me when I log in remotely using Teamviewer and Quickbooks was already running on the computer prior to remotely logging in. It is obvious to me that Quickbooks is running, as I can see it in the taskbar, but I cannot access the window or maximize it. When I am sitting in front of the computer working directly on it, I have never experienced this issue.

Here is how I fixed it:

1) Press CTRL+SHIFT+ESC which will bring up the Task Manager. You can also reach the Task Manager by pressing CTRL+ALT+DELETE and then clicking on Task Manager.

2) Locate "Quickbooks (32 Bit)" on the list. Right click on it and select "End Task". This will close Quickbooks completely. (See picture below)

3) Leaving the Task Manager open, Re-open Quickbooks. You should see "Quickbooks (32 Bit)" reappear in the Task Manger. (See picture below)

4) Locate the little arrow to the left of "Quickbooks (32 Bit)" which will expand when single-clicking on it. (See picture above). Once expanded, you will see "Intuit Quickbooks (Your Version)". Right click on "Intuit Quickbooks (Your Version)" and select "Bring To Front". Then right click on "Intuit Quickbooks (Your Version)" again and select "Maximize". This will resolve the issue. Now you can close the Task Manager and work in Quickbooks.

Good luck!