If your wireless keyboard does not work, check the followings:

Battery failure. The transceivers attached to the computer are powered by the computer, but the input devices themselves are battery-powered. If your unit isn't running as long as it should, try using a better brand of battery or turning off the device if possible.
 

Lost synchronization between device and transceiver. Both the device and the transceiver must be using the same frequency to communicate. Depending on the device, you might be able to resynchronize the device and transceiver by pressing a button, or you might need to remove the battery, reinsert the battery, and wait for several minutes to reestablish contact.
 

Interference between units. Check the transmission range of the transceivers in your wireless units and visit the manufacturer's Web site for details on how to reduce interference. Typically, you should use different frequencies for wireless devices on adjacent computers.
 

Blocked line of sight. If you are using infrared wireless devices, check the line of sight carefully at the computer, the space between your device and the computer, and the device itself. You might be dangling a finger or two over the infrared eye and cutting off the signal—the equivalent of putting your finger over the lens on a camera.
 

Serial port IRQ conflicts. If the wireless keyboard is connected to a serial port and it stops working after you install another add-on card, check for conflicts using the Windows Device Manager.
 

Disconnected transceiver. If you have moved the computer around, you might have disconnected the transceiver from its keyboard, PS/2 mouse, serial, or USB port. You can plug a USB device in without shutting down the system, but the other types require you to shut down, reattach the cable, and restart to work correctly.
 

USB Legacy support not enabled. If your wireless keyboard uses a transceiver connected to the USB port and the device works in Windows, but not at a command prompt, make sure you have enabled USB Legacy support in the BIOS or use the PS/2 connector from the transceiver to connect to the PS/2 keyboard port.
 

From www.freeopenbook.com