Windows Explorer not showing C: drive root

I have a 2 yr old Win XP PC P4 and when I open Windows Explorer and try and find the C: drive (the main drive) the icon showing it’s looking thru folders comes up and never stops looking. I can see My Documents and anything but the C: drive. If I go thru RUN I can see it but not using windows explorer.

How can I fix this annoying problem?
Is it something to do with paging or ram?

Thanks
Bruce