Why do I keep getting "connection lost" when I begin work on my desktop Apple

I have an IMac desktop computer about 5 years old now. It has been updated very recently. As I begin working with my mouse I get a "connection lost" signal and it is becoming more and more frustrating since I basically have a frozen arrow. I have taken the mouse in the Apple store and they say it isn't a mouse problem. I've changed batteries in the mouse. I've tried a new mouse. Is there something wrong with the hard drive? Help