Screen Saver Won't Come On (HID Non-User Input Data Filter..

Hi,
I've got a Dell E520 running Vista HP SP1, fully updated. I am using
a Mircosoft Wireless Notebook Optical Mouse 4000. My screen saver is
set to come on at 15 minutes, but it won't come on. I've even
installed the HID Non-User Input Data Filter.
What can I try next?

One more thing, why does my "Installed Updates" window show different
updates than my "View Update History" window? I just noticed that the
HID Update does appear in my View Update History as

"Microsoft - Other hardware - HID Non-User Input Data Filter
Installation date: ý2/ý2/ý2009 12:38 AM
Installation status: Successful
Update type: Optional
Microsoft Other hardware software update released in November, 2008"

but doesn't appear in my Installed Updates.

Thanks.