USB Driver installation

I have a Dell Precision T3500 workstation and cannot get the USB drivers to install. However I try the installation system claims that the most suitable driver is already installed. This is just not the case, I have found the driver directory and all attempts to load what appears to be the correct driver fail.
It always installs a driver for the MEGA 2560 on COM 3, this is the correct board but not the right driver I found this after trying to use the serial monitor which should appear on another port but doesn't.

The serial monitor will appear on COM 3 unless you are using one of the megas other ports to output to something else.

Maybe post screen shots of the actual errors you are seeing.