The way I got the drivers installed for my nexus 5 was by following these instructions but I had to turn off my phone and do the steps below but for following the first set of instructions for the link below:Nexus 5 Driver installation instructions
power off your phone.
press and hold Volume Down and Power buttons simultaneously
- an Android robot will show up and the Fastboot Mode text is listed.
connect the Nexus 5 to your PC via USB Cable.
After doing this the drivers installed but had a yell warning sign. However I was still able to get it to take commands and for it to be seen by the ADB devices command. I currently am using windows 7, and I have the adb setup in my environment variables so I can run commands from the command line.
In the command line before you call the adb devices, make sure you navigate to the android platform tools folder '\Android\android-studio\sdk\platform-tools then from here call the adb devices and you will know for sure if your device is being detected!