[Nexus 4 Q&A, Help & Troubleshooting] bett3rthan:
Are you getting errors like "device not found" or "device offline" while trying to run ADB commands? Here's a quick way to troubleshoot your problem on Windows.

Steps

1. Ensure USB Debugging is enabled in Developer Options.

2. Verify current Google USB Driver is installed and that Device Manager is using that driver.

3. Update to latest version of ADB.

1. Ensure USB Debugging is enabled in Developer Options.

Enable Developer Options by going to Settings -> About Phone and tapping on "Build Number" multiple repeated times. You will be greeted with "You are a developer."

Now, under Settings -> Developer Options, ensure you check the box for "USB debugging."

2. Verify current Google USB Driver is installed and Device Manager is using that driver.

You may skip this step if Device Manager lists your phone as "Android Phone -> Android Composite ADB Interface." If it does not, this is likely your root cause.

Go to the Google USB Driver page and download the latest driver directly from Google. Extract the zip file to a folder you know and will remember in the future.

Open up Device Manger in Windows with your Nexus 5 connected. Whatever your Nexus 5 is currently detected as, right click on it and select Properties. Then, in the Driver tab, hit "Uninstall." If available, select "Delete the driver software for this device." and hit "OK." It will remove the old drivers.

Restart your computer.

After restarting, reconnect your Nexus 5. It should be recognized as an unknown device in the Device Manager. (If it isn't, try the previous driver deletion steps again.)

Right click on the unknown Nexus 5 device, choose Properties, and in the Driver tab again select "Update driver." Browse your computer manually by putting in the path to the new Google USB Drivers you unzipped to a folder of your choice in the beginning of this step. Choose next and your drivers should install! You'll know everything completed successfully when you see the phone listed under "Android Phone -> Android Composite ADB Interface" in Device Manager.

This is the most finicky process, so don't be afraid to reboot your computer a time or two and repeat these steps if they don't work on the first try.

3. Update to latest version of ADB.

This is a crucial step. The new version of ADB is required to work with the "USB debugging authorizations" setting.

Perhaps you know how to update ADB, in which case, just do it. However, here's a detailed manual approach to download JUST the adb suite from the SDK:

Go to the Google Android SDK website and choose "Use An Existing IDE" and click the "Download the SDK Tools for Windows." This will allow you to download only an 80 MB file rather than the whole 400 MB suite.

Install the SDK tools exe to a folder of your choosing.

Run SDK Manager and uncheck everything except for "Android SDK Platform-tools." This is the ADB and Fastboot bundle. Install that.

Navigate to your SDK Path as indicated at the top of your Android SDK Manager window. You will now see a freshly downloaded platform-tools folder containing ADB.exe, Fastboot.exe, and a host of other files. That folder is now your updated, portable ADB tools folder. You can move it anywhere you like as long as you run ADB from a command prompt window set to that directory.

After you've followed these procedures, running "ADB Devices" should trigger a prompt on your device to accept the RSA fingerprint of your computer. Accept it, and now all should be working as intended!

Questions? Ask below!

Thanks to:MaxRabbit