System Tray missing!

I've just got a new PC at college (running Windows XP Home Edition) and, even though my system tray was fine when it was first set up, all the icons are now missing. The clock is still there, but icons such as Trillian and Skype do not appear - I can't access Trillian at all, as (for some reason) it's starting minimised. Pop-ups like mail notifications still appear.

What strikes me as odd is that, when I right-click on the taskbar and select properties, "Hide inactive icons" is not only unchecked (I previously had it checked), but is also greyed out so I cannot check the box. "Customize" is also greyed out. Can anyone suggest what the problem is?

 

I found this while searching similar problems:

 

You could try this....

http://www.tech-pro.net/howto_013.html