I wanted to enable the HomeIP applet but it did not show up anymore. Same with Mchronos. After setting the applet check mark from the home screen they did not show up and opening the applets window showed them still unchecked. I uninstalled and reinstalled homeip but that did not help.

What can be the problem here ?

Do you have any non-standard taskbar applications currently running?

When the hildon-desktop process crashes it'll take your home applets and taskbar applications with it. I think it can also cause this behaviour.

As per this thread you can reboot, or follow Nelson's advice to do it without rebooting.