Windows Vista Ultimate, strange problems.

My System Specs
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System = Dell-XPS-Gen-3

Memory = 2558MB (RAM)

Hard-Drives = Weston Digital 500gb Weston Digital 250gb both Sarta drives and the third 150gb is IDE.

CPU = Pentium 2cpu 3.19ghz

GFX = Nvidia Geforce 7600 GS

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Problem
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The problem I seem to be having is that my taskbar and quicklauch tool bars seem to stop working and can't use them at all until I press ctrl alt and del and then return to windows.

My second problem is disk defragmenttation I try and click on the button in hard-drive properties but nothing happens.

Any help would be great! thanks.

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2558 ram makes me wonder exactly what configuration your using
2X1 gig and 1 512 ?
try it with just 2 gigs