I don't think that using "Taskbar Repair" (presumably a third-party
application) to "mend" the problem.
If what I think you are saying is that, every so often, when you hover
your mouse pointer over icons in the System Tray (Notification Area),
you no-longer see any of the usual "balloons" ?
Although, you are incorrect in calling these things "balloons" as they
are called "Tool-Tips" and are different from "balloons" which are also
called "System Notifications".
My system, also, has this "problem" from time to time, and is usually
caused by a window, be it a visible or a hidden window, stealing
temporarily, the desktop focus so that the "Tool-Tips" display at a
level that isn't visible.
If you ignore it when it happens next, I think you will find that the
Tool-Tip function returns after a further ten minutes, or so, of normal
computer usage (as you start and / or close other applications, the
desktop focus will return to a level so that the Tool-Tips will again be
visible).
It is not usually a permanent thing, but just a transient irritation
like much of the weird and wonderful ways of WinXP!
==
Cheers, Tim Meddick, Peckham, London.