VirtualBox: Windows 7 says it's not genuine

To start the Product Activation Wizard, follow these steps:

1. Click Start Button
2. Right-click Computer.
3. Select Properties.
4. At the bottom of the window, click Activate Windows now.
   

In the Product Activation Wizard, follow these steps:

1. Click Use the automated phone system to activate

2. Click the drop-down menu, select the location that is nearest to you, and then click Next.

3. The Product Activation Center telephone number is displayed under Step 1.

For more information about how to activate Windows 7, go to the following Windows Online website:
Activate Windows 7 on this computer

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Just an added note, sometimes the phone system will tell you that you have installed this key the maximum number of times. It will then ask you how many PCs are running that copy, and you can say "zero", which will allow you to proceed with activation.