|A couple of things:|
Firstly, when you type
make sure there are NO spaces around the equals-sign.
Secondly, when you drag-n-drop the installer to the command prompt, make sure you do that just after you type in the above SET commands, as the effect of those command is only temporary and only lasts for that window.
If the above doesn't work, try the following. Instead of being in C:\ at the command prompt, go into the folder where the installer is. You do this by typing CD /D then a space and then the name of the folder where the installer is. Once you've gone into that folder, type