The web client is working for everyone else, Marioanius, so, if you're still getting this problem, it's something on your end.
Is this the same browser you were using back when this used to work for you or have you changed browsers since then?
Have you done things like quitting and restarting your browser? Clearing its cache? Trying a DIFFERENT browser?
Have you tried the "private", "anonymous" or "incognito" mode in whatever your browser of choice is? (ALL modern ones have this feature.)
Have you tried using the HTTPS instead of HTTP version of the webclient webpage? (Either click the "Lock" icon next to the webclient login form, or, just edit the address in the browser bar so it says https:// instead of http://)
Have you tried doing what we call a "hard refresh" on the screen where you're getting the blank? (Hold down the shift key while doing refresh with the browser's reload button, or, hold down the shift key while doing [ctrl]+[r])
While on the webclient login page, before clicking the "Connect" button, have you ever been presented with a browser warning about a security certificate? If so, did you choose to obey the warning or did you choose to instead proceed anyway despite the warning? (Hint: Do the second.)
When the server needs to have its webclient app restarted, the symptom is USUALLY different than this blank-black-screen problem (you usually see a white screen with a "too many open files" error in black text), and, it affects many people until it's resolved, not just one person persistently.
This is why I recommend trying as many things as we can think of to figure out what's going on on your end. Because, the webclient is fine for everyone else right now, and, there's nothing we can restart or poke in order to fix your problem for you. But, we can help you brainstorm.
See if any of this helps.