There are a few things that you can check. Since the RF receiver uses an active port (usb) did your computer have any issues detecting the mouse and keyboard? Were there any problems installing the SetPoint software?
In your bios what are your settings for usb devices - legacy usb?
The MX Engine uses Fast Rf - that's 2.4 mhz. There are a number of electronic devices that also use that frequency - wireless speakers and cordless telephones come to mind. Having items like that in the vicinity of your keyboard/mouse can do a number of things - from preventing your mouse or keyboard from operating, preventing them from being discovered by the computer, mouse drag, key repitition, etc.