After we updated plesk on one of our debian servers to the newest version, we where unable to open the plesk login page. The page simply timed out without an error message.

To fix this we opened a SSH terminal access to our server and used the command:

ps auxxf | grep install

There we got a list of our initial grep command, followed by some hanging plesk installers.

From there we took the PID (the first number shown) and killed this processes with:
kill

We did this as many times as there where plesk installers runnning.
Now we tried to open the plesk login page again and it worked again!

Plesk installers seem to often hang for various unknown reasons.