Why won't my Nokia Lumia 800 be recognized by Zune?

I bought a Nokia Lumia 800 last week. I plugged it into my computer after downloading Zune and it kept saying "no device connected". I have done everything the Zune website and Windows website said and still nothing. When I plug in the phone the Computer recognizes the phone and the phone charges. The Zune software never came up before today but when i deleted the the software and downloaded I really thought it would work, now when i plug the phone in the Zune software comes up automatically. I have Uninstalled it then re installed it and still nothing. I brought the phone back to the shop today and they just said come back on Friday and talk to the Manager and he will give a new phone, but the catch is they have to find a fault with my phone to give me a new one. They are not getting the Nokia Lumia 800 phones anymore so it won't be a straight swap, i like phones and don't want to swap it but i will have to if they do find a fault. They said that there has been problems but they all have been fixed.

Please help me I am desperate at this stage.

Thanks in Advance! :)