We're going to need a bit more info. There is a potential bug in the windows installer for the beta client on Win 10. That could be it.

Have you checked to see if any f@h processes are running?

No processes running, I had it working for quite a long while and it just quit a couple days ago and refused to run. I'm on Windows 10, fully updated. It used to start with Windows, but now even when I double click the icon it thinks for a split second but there is no response beyond that, no processes that come up, nothing in the tray.

Maybe start with looking in C:UsersusernameAppDataRoamingFAHClient
It should contain 5 folders and 5 files including some logs and the most recent will be in the root there, you might find some clues in those log files or can copy / paste that log into a

 code space

we may be able to help.
Next programfiles/fahclient to see if its empty. If any of these are empty than I would suggest reinstalling the program completely. If the appdataroaming has works units you can copy them and try to salvage them.
Let us know what the progress is