Hi V frustrated. Welcome to the Forum.
The biggest problem people have with wireless components is signal interference/signal degradation. This is caused by other wireless devices or devices that produce an electromagnetic field that extends into the space between the device and the receiver. The most common culprits:
- Wireless speakers
- Computer power supplies
- Computer monitors
- Cellular telephones
- Cordless telephones
- Garage door openers
You can also get weird interference when using the devices on metal surfaces.
If you are sure there are no other devices that could be interfering with the keyboard and mouse then you could try resetting the devices.
If your wireless devices are more high end they will have the capability to be resynchronized. See here: http://support.microsoft.com/kb/838398
If there is no synch option then my approach would be to completely uninstall the receiver from Control Panel > Remove Programs and/or the Device Manager, restart the computer, find and download the most current version of the driver, and install everything fresh with the newer driver.
And check the batteries again (try a new set). It is not unheard of for batteries to be dead in the package.