Open an admin tool, and check that the web server is running.
If not, click on "Restart Web Server".
If the server won't start, make sure you have not installed another web server or application that would be using the TCP port 80 and/or 443 (Skype and Teamviewer for example).
One easy test to do is to change the port of your webserver and restart the server again.
A faq regarding this subject is available here: https://support.tsplus.net/support/solutions/articles/44000037656-how-do-i-change-the-port-of-the-web-server-
Make also sure that your firewalls and / or antivirus (software or hardware) are not blocking port 80 and/or port 443 or any TSplus processes located in these two folders :
C:\Program Files (x86)\TSplus
Open a browser on the server, type in the address http://127.0.0.2 and open a connection using the RemoteApp or html5 mode. You should be able to open a session with a local or domain account.
If it still wont connect, uninstall java and delete the java folder located in C:\Program Files x86\ and C:\ProgramData (this is a hidden folder) then reinstall java 64 bits on the server and make sure antivirus or firewall software are not blocking svcweb.exe process.