When using a modified inf file with drivers the modified inf must have the following characteristics: a) It is for the same operating system as the driver you downloaded. b) It must be for the same number of bits (32 or 64) as the driver you downloaded. c) It must be for the same language as the driver you downloaded (English USA and International are different languages). 1) Download the 267.59 driver from the NVidia downloads section and you'll only find it for the 550 Ti card. 2) Next try to install it (notice where it is going to extract the drivers to) and let it tell you it can't do it. Then you say OK and if Windows asks if it installed ok you say yes. 3) Then you take the modded inf file and paste it into the Display.Driver folder where your 267.59 drivers extracted to during the installation attempt. Windows will say a file of that name is already there and asks you if you wanna overwrite it and you say yes. 4) Now you're ready to find the setup.exe file in the folder where your 267.59 drivers extracted to during the last installation attempt (not the original file you downloaded) and double-click that setup.exe file and installation begins.