I still haven't given up. It seems to be a problem with what we call the "layout" of the controls in your session. No one that I know has seen this issue, so we are shooting in the dark here, I'm afraid. Here are a couple more last-ditch things to try:
1. Randomly try turning things on and off in the View menu:

Just do things like turn the browser, comments, Navigation Bar, etc on and off a few times, followed by more "Reset to Default Layout", etc. The idea here is to kick the layout into submission.
2. Clear the user cache data. This is a command under the help icon in the upper right hand corner:

This shouldn't have any effect, but we're getting desperate.
3. Finally, the nuculear option. I'm not exactly sure here where these files are, because my computer is also a development machine, and has had a lot of old versions installed on it. But, I think this is where things are stored:
3a. With Fusion not currently running, open up a windows explorer window.
3b. in the address bar, type "%appdata%" (not the quotes)
3c. navigate down to "Autodesk\Neutron Platform\Options"
3d. there should be a folder there with some random characters. On mine its "\GFYCRMPLKPEB". go into that folder
3e. one more level, to "options"
there should be a file there called "NULastDisplayedLayout.xml". If you can, send this file to me in a private message. I'd like to see what's in it. This is a description of your app's UI layout. If you are curious, open it in a text editor. There is an entry there for the timeline. Mine looks like this:
<Area Contents="Timeline" InternalPadding="25,4,4,4" Name="Timeline" Placement="Bottom" Rect="0,1276,50,0" Resizable="False" Stretchable="True" Visible="True">
If anything looks bad in there (like Visible is not true, or the rectangle is tiny, or in some strange place), that is probably what is going on.
At any rate, this file is not necessary. It will get generated when you start up the next time, if it is gone. So, just delete it. Or, rename it to something else (safer). Then try starting Fusion again.
If none of this works, we may have to try a screen-sharing session, so I can poke around your system and try to repair it.
I appreciate your patience.
Jeff
Jeff Strater
Engineering Director