The new F165 and new FSCANs with USB connections often have difficulty communicating with your computer. I have seven F165s and they all have given me considerable trouble by dropping offline unpredictably.
Using a driver analysis program called Driver Detective, I discovered that the Microsoft USB drivers were out of data on all five of my computers. These drivers are included in the lastest mouse software from Microsoft which you can download at the Microsoft Mouse and Keyboard Hardware site.
You don’t need Driver Detective which has a fee, but you do need the latest Microsoft drivers which are free. If you are running Windows XP using the English language, the name of the latest file is IP55_32Eng.exe.
These drivers appear to have resolved all USB problems on all of my computers.
Please note that these drivers are independent of the USB drivers that come with the F165 and FSCAN which must still be installed properly. The Microsoft drivers provide the infrastructure that interacts with the F165 and FSCAN drivers that come with these frequency generators.