I can't shutdown XP

[Ed]

A couple of weeks ago, I changed a setting (can't remember
which one) which slightly changed the colors on my desktop
(made them softer). Since then, I can't shut down. I
will go to turn off computer and the standby mode is
faded, and when I click on shutdown-it just restarts-every
time. So I have to shutdown just before restart by using
the power button.

Help!