If your ActivBoard is not responding to your computer and you have a red cross  on your ActivManager icon, this means that the ActivDriver is not able to detect the ActivBoard.
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Before you begin, ensure that your ActivDriver is up to date by downloading the latest version from the ActivDriver support page.

Occasionally, ActivDriver doesn’t update the Windows device drivers. Right click on My Computer, select Manage and then select Device Manager. Locate Human Interface Devices.

If you see a device with a yellow exclamation mark, you can resolve the error by manually updating the device driver. Right click on the device and select Update Driver Software.

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This will run the Update wizard. Select Browse my computer for driver software. Windows XP users will need to select No, not this time and Install from a list or specific location.

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Copy and paste this file path C:\Program Files\Activ Software\ActivDriver\activusb\XP into the search box. This path is valid for all versions of Windows. Alternatively, click Browse and navigate to this location.

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Click Next to begin the update.

Once complete, the ActivBoard will be detected by the computer and the ActivManager icon will no longer display a red cross. You may wish to calibrate the ActivBoard before use.