Some BIOSes do not correctly detect all keyboards. Updating your BIOS to the latest version should address the issue. If it doesn't, please contact our support team with the manufacturer and model number of your motherboard, and we can assist the manufacturer with an updated BIOS to correct the problem.
You can find a link to the latest firmware (version 2.11) here. The zipped file contains both the latest firmware and software versions for the K90. Double-click the firmware update file and follow the on-screen instructions. The firmware update may take up to a few minutes, and will display an update successful message upon completion.