USB external hard drives serve as storage tools for important files that numerous people utilize. When you attach your USB drive to the system sometimes serious issues can pop up. You may encounter a notification stating: "USB Device Not Recognized". This happens when you already have a USB device connected to your system. 

The issue becomes a nuisance but it has multiple solutions available to you. The issue can be resolved through multiple approaches.

Why Does This Happen?

Multiple conditions lead to this error which include:

1. The program running the USB driver shows signs of instability due to corruption.
2. Your computer needs an update.
3. Windows is missing important updates.
4. USB controllers have become unstable.
5. The external drive operates in a selective suspend state.
6. Your computer needs updated drivers for its motherboard component.

The following section presents straightforward methods to resolve this problem.

Solution 1: Uninstall and Reconnect the USB Drive

A situation can develop where the USB driver loses its stability. Follow these steps to fix it:

1. Start your search by entering Device Manager through the Start interface.
2. Use Device Manager to open the Disk Drives section.
3. Right-click on your USB external hard drive and select Uninstall.
4. Wait for one minute after removing the USB storage device.
5. After waiting for around a minute reconnect the USB device. Windows will automatically reload the driver.
6. Look for your USB drive in File Explorer to verify its appearance.

Using a non-powered USB hub should be avoided at all times. Attach your USB drive by inserting it directly into your computer.

Solution 2: Install Windows 7 Hotfixes.

Users of Windows 7 require additional specific updates to perform correctly.

1. Open the Microsoft website to search for and find the KB976972 update file.
2. Users should choose and download a Windows update package that matches the operating system version they are running on their computer.
3. To determine your system type open Computer then right-click Properties for the Windows version number.
4. Open the download option followed by an onscreen guide to execute further instructions.
5. Restart your computer.

After obtaining the KB974476 hotfix start the installation by following the same procedure.

Solution 4: Reinstall USB Controllers

Sometimes, USB drivers become corrupted. Reinstalling them can help.

1. Click Start and type Device Manager.
2. Expand Universal Serial Bus controllers.
3. Right-click each USB device and select Uninstall.
4. Restart your computer. Windows will reinstall the USB controllers automatically.

Solution 5: Disable USB Selective Suspend

Windows may be turning off your USB drive to save power. Here’s how to fix it:

1. Click Start and type Power Plan.
2. Select Choose a Power Plan.
3. Click Change Plan Settings. You can spot this option just next to your active plan.
4. Click Change Advanced Power Settings.
5. Expand USB Settings > USB selective suspend settings.
6. Set Plugged in and Battery to Disabled.
7. Click Apply > OK.

Still Not Working? Contact Microsoft Support

If none of these solutions work, you may need help from Microsoft. Visit their support page for further assistance.

If none of these solutions work, you may need help from Microsoft. Visit their support page for further assistance.

Start from the first fix and then, gradually proceed, making sure that you don't miss out on any major fix in between.