They will tell you to use a different port,
uninstall the logitech setpoint software and reboot,
try the mouse on a different computer if possible.
Then, if it is a problem they see all the time they will ask for serial numbers to see if it is under warranty. Sometimes they will ship a new one, sometimes ask you to ship back the defective one.
As an aside, a funny thing happened after I gave the serial number and got put on short hold. When the rep got back to me to give me the RMA#, he says he needs the S/N off the receiver as well. I reply, "there is no receiver, its a corded mouse." He says, its a G5, right?. I say, "yes, the G5 is corded, the G7 is wireless". He starts to argue politely to try to explain to the newb about how wireless mice work, then stops. Ooops
Anyway, I shipped the mouse sans the weight set for $2.79 postage and should get a new one hopefully within 7-10 days.