HELP!! lost partial administrative privileges!!

Archived from groups: microsoft.public.windowsxp.security_admin (More info?)

This is a wierd problem that I have encountered in the last 2 days.
I am the adminisrator on this computer. Since yesterday it wont let me
access the calender (by double clickng the time icon in systems tray).
Someone suggested earlier to go through the following path to corect this
problem

Control Panel --> Administrative Tools --> Local Security Policy -->
Security Settings --> Local Policy --> User Rights Assignment

Although if i do this the comp freezes up at "User Rights assignment" stage.


Also it wont let me add any hardware. ("You donot have sufficient security
privileges to install or uninstall devices on this computer" )
But it lets me download and install programs on here. Also I can add and
remove programs.
I can also create and delete new user accounts!
Any ideas why this might be happeneing?? And any possible solutions