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This is a fun issuer I can into, but gladly I had the keyboard working on the Windows 7 computer that I was fixing. This can be caused by the “Allow the computer to turn off this device to save power” setting being Enabled in Device Manager. Below is a direct copy (Click here for the Original Post) from the Microsoft Community discussion that solved this issue, but be warned it has solutions that involve editing the registry (doing so incorrectly can cause serious issue with Windows) so you should always backup the registry before starting any changes in the Windows registry (See Microsoft KB 322756 for more information):

Perform these steps and check if it helps.

1. Click Start, type Device manager in the Search box and then click Device Manager from the returned list
2. Click to expand USB Root Hub and click the Power Management tab
3. Uncheck the option to Allow the computer to turn off this device to save power and click OK

Note: You may see multiple listings for USB Root Hub, uncheck this option for all USB Root Hubs.
Close the Device Manager

Advance steps would be modifying the registry.

1. Click Start
2. type regedit in the Start Search box, and then click regedit in the Programs list.
3. Locate and then click the following registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Executive
4. In the details pane, right-click AdditionalCriticalWorkerThreads, and then click Modify.
5. In the Value data box, type 2, and then click OK
6. Note You can specify a value that is between 1 and 16.
7. Exit Registry Editor.