Hi,
· What changes were made to the system between the time everything last worked and when you noticed the problem?
· How long have you been experiencing this problem?
· Did you try plugging into different USB port and check if it has the same issue?
Follow the instructions the link below which might help you in resolving the issue.
Method 1:
Try downloading and installing the latest updated keyboard software from Microsoft Website and check if the issue is resolved.
http://www.microsoft.com/hardware/download/download.aspx?category=MK
Method 2:
Troubleshoot response failures in wireless keyboard or mouse
http://support.microsoft.com/kb/838398
Hope this Helps,
Thanks and Regards, John S Rubdy – Microsoft Support