Access is Denied

I have Dell Dimension 9150 Windows XP SP2 and recently I received an ATI
video driver error requesting an update so I tried to upgrade the driver. I
received an error during update and Now I get VGA standard graphics only and
it will not let me install any drivers even following directions from the
support site from dell and ATI. I have 2405FPW monitor. ATI radeon x300 se
128 mb hypermemory and its secondary. Under device Manager, I have video
controller, and video controller (VGA compatible). Original error message was
"Set up was unable to complete the installation. Try to set up your display
adapter with a standard VGA driver before running set up." Now the error I
get is Cannot install this hardware. An error occurred during installation of
the device. Access denied. I have administor privilege. All virus and spyware
program is turned off. I cannot seem to fix it no matter what. Have tried in
safe mode also.