Can you please try the troubleshooting steps below:
1. Do “Rescan servers”.
on MT4, Click on File > Open an Account > Click on FusionMarkets-Demo> Scan
2. A simple MT4 restart might solve the problem.
To restart MT4 you simply need to click the X at the top-right corner of MT4 window, or go to top menu “File->Exit“. Once your MT4 is closed I recommend waiting at least 30 seconds before you open it again. This will allow MT4 to update all necessary files on exit.
3. Try to log in to your Demo account again.
Simply go to “File -> Login to Trade Account” in the top menu and then click OK when the login window appears. Login, Password, and Server should already be filled in if you were logged in successfully last time.
See the attached file for the basic troubleshooting steps