Having a halogen lamp with a dimmer on the same circuit as your computer can bring you hours of fun!
Seriously though, if there is no obvious sign of interference you might want to open the box and reseat all cards and cabling; perhaps moving it is just making/breaking a weak connection somewhere. If that doesn't help, I'd move it to yet a third location as a test. If it works in two out of three places, you'll need to examine the power/electrical situation of the problematic location more closely.
BTW- these are just your basic, wired flavor of mouse and keyboard (no wireless/IR stuff going on), right?