It happens sometimes, you plug the phone in the computer and it wouldn’t get recognized. It just keeps asking you to plug the phone though it’s plugged in. The problem is that nothing helps, replugging into another port, reinstalling the phone’s desktop app, restarting the PC, plugin with the phone’s screen unlocked.
The last solutions to try:
1. Power off the phone & wait till it turn’s 100% off. Now connect it to the PC. The phone will turn on automatically and it should be detected. Drivers should also load automatically.
2. If the above solution didn’t worked, try again to Power off the phone then pull out the SD card, connect the phone to the computer and turn it on. Wait till the phone is detected and the drivers are loaded.
If the above solution worked, this means your SD card is damaged. Open it with an SD Card Reader, back up your files and format it. Now try again to boot the phone with this SD card, if doesn’t boot this means you need to get another card.
3. Reinstall drivers. Connect your device to the computer, Right click on My Computer, click Manage and select Device Manager (or go to Control Panel > Hardware and Sound > Device Manager), locate and select Nokia Phone (Lumia Phone) in the right pane, Right click on it and select Uninstall. Wait till drivers are uninstalled. Unplug your phone, power it off and plug it again. It should automatically Power on and install drivers.
4. Borrow from a friend a Nokia USB cable and try to connect your phone with it. If it works, get another USB cable.