I'm running a fully updated Windows 2008 system. Every time I try install drivers recently, I always get 'Access denied' as an error message. I am unable to install a lot of new drivers, update existing ones, or even run automated driver installers (i.e. from nVidia). I am logged in as Administrator.

When I removed my video drivers, the only way I was able to get them reinstalled was booting into safe mode, where Windows installed them. Unfortunetly, it only installed the old drivers. Even after that in safemode, I couldn't install the newer drivers using the nVidia installer, or manually pointing to the drive, as I'd get the same 'Access denied' error message.

Is it possible that the user named 'Administrator' is removed from the 'Administrators' group? You can check this by entering lusrmgr.msc in Start -> Run, and see in the Groups section if the Administrators group contains the Administrator user.

Besides that you can try if setting the User Account Control (Start -> Control Panel -> User Accounts -> Change User Account Control Settings) option is set to Never Notify to avoid UAC blocking the installation of the drivers.

Finally, if these options doesn't work out, try to find out using Sysinternals Process Monitor what is bothering the installation of the drivers.

Hope this helps you and good luck with this weird problem!