I see that you have FW3.60,this mean that you never use webupdater on this nuvi?
If you use webupdater and now you have 3.60 then your chip is faulty.
Do you install usb drivers on Pc with XP and then open updater.exe and add dot beside USB,go to preboot and flash?
Updater.exe recognize your nuvi model in window beside USB in updater.exe?