Tried installing Em Client today (latest version). It downloaded and installed fine but it didn’t open. Just sat in the background processes in task manager. Uninstalled, reinstalled… same problem. Tried everything in safe mode… same problem. Tried downloading and installing version 6… same problem. Any ideas? 
If you kill the process, can you then successfully start the client?
The uninstall process does not delete data files. If they are somehow corrupt, this can cause a problem. To do a clean install, delete the following directory after uninstall:
c:\users[user_name]\Apps\Roaming\eM Client (Hidden folder-- make sure to enable “hidden items” in Windows Explorer view menu).
Yes, tried both of these and it still doesn’t open. I now get a database check window appear but nothing happens after that closes.
The database check occurs when the program is not shut down in a normal way. Often, this can be because a program is holding on to the database and keeping it open. Typically, this is an anti-virus program. Try disabling your AV program and see if the problem continues.
I would again delete the data files so as to have a fresh database (eM Client creates a new, fresh database if one is not present).
Thanks but tried that and still nothing.
However, I have finally managed to get it to open. To do this I did a clean install, restarted in safe mode, ran eM Client. It took a while but it finally did open in safe mode. Restarted into normal Windows 10 mode and eM Client now opens fine.
Thanks for your advice anyway.