Tried everything, ADB is not detecting my nexus on windows 7

I'm trying to add my external device(nexus 5) to test. for that
1) I have installed Google USB drivers
2) set environment variables as ANDROID_HOME & PATH
3) set android:debugger="true" in manifest, same in gradle.
4) if I list devices connected to ADB in command prompt, gets no devices.
5) Driver for nexus 5 is uptodate as i have checked from device manager of windows 7.
6) enabled usb debugging on my phone in developer options.

It seems nothing is working on my way here, how can I test my camera/bluetooth app on my nexus 5? please, help.