Can't install drivers Windows 7

I am using an Arduino Mega ADK, and my computer is Windows 7-64 bits.
I used my Arduino on other computers and it worked perfectly.
I tried everything, turn off UAC, antivirus; but when I try to update the driver error occurs Access Denied.
please help, I'm going a month without solving the problem...

Sounds like you need administrator rights for your computer?

I have administrator rights..actually im the only user of the computer....