Garmin Nuvi 760 wont talk to computer

Hi everyone hope someone with some Garmin / PC technical background can help me.

I have purchased a Garmin Nuvi 760 and have been unable to get mp Windows XP PC to recognise the GPS as anything other than a removable drive. I can not use map source or any other software from Garmin as the drop down to select a GPS does not show the Nuvi for me to select.
I have uninstalled re-installed re-booted over and over but just cant get it to load as anything more than a disk drive. I downloaded the driver software from Garmin website and it gets half way through tells you to turn on and connect the GPS which I do, only to get an error message telling me to turn on the GPS. I presume it is something in my windows setup just seeing the mass storage device and not the full product.
I rang Garmin help desk today and after 29 minute wait spoke to a very helpful Tech who thought he had fixed the problem by allowing windows to see the file extensions in the Garmin folder on the Nuvi, he hung up after starting a firmware update for me and they were closed by the time I worked out it hadn’t fixed the problem.

Any suggestions ???? I have spent hours now ….. Happy to supply more info if you think you can help