Why does clicking "customize" on the system tray do nothing on my computer?

"We are going to restore your Notification Icons area functionality. Hopefully this fixes the problem, whatever it may be.

Because we are going to play with the registry, first thing to do is to make a backup copy of the registry you can later restore if anything goes wrong:

Click the Start Button and type
systempropertiesprotection. Press Enter.
Answer to the UAC prompt(s) if they
show up.
On The System Properties dialog, you
should be looking at the System
Protection tab. Click the Create
Button.
Type a name for this restore point and then click Create. If
System Restore is currently turned
of, you will be asked about it and
should answer accordingly so that
System restore becomes active and
this restore point assigned to your
Windows partition.

If anything goes wrong with what we are going to do with the registry, here's how to restore your system:

Click the Start Button and type
systempropertiesprotection. Press Enter.
Answer to the UAC prompt(s) if they
show up.
On The System Properties dialog, you
should be looking at the System
Protection tab. Click the System
restore Button.
Select the Choose a different
restore point option and click
Next.
Select the restore Point you
created previously and click
Next.
Click Finish and your system
will be restored.

So, let's start by try and rebuild the information on the Icon Notifications area.

Fire up regedit.
Navigate to
HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\CurrentVersion\TrayNotify
Delete the IconStreams and
PastIconsStream keys.

Now, the most important, albeit not very common process: This has to do with how Windows uses the Icons Notification area and how it creates and populates these keys.

Open Task Manager
Right-Click Explorer.exe and
select End Process from the popup
menu.
Still on Task Manager, click on the
File Menu and select New Task (Run...)
Type explorer.exe and click Ok.

Why do this? Because forcing explorer to restart will ensure those two Keys we deleted are also removed from memory and not put back in place against our will when we do the next and final step. So, one last step:

Logoff and log back on.

This will generate those two keys again and populate them only with applications currently on your tray icons area. Essentially it recreates the Icon Notifications list with a cleaned list. Your current problem is almost probably to do with corrupt data on one of these two keys, so this should fix it.

Let me know if it now works."