Web Cam woes

[The Doctor Alt 8]

I bought (For the second time) a Logitech Streamcam in the last Amazon sale. I've connected it up but.... there is no indication that it's working. Website claims that as soon as it's connected to the PC it should download it's drivers and be ready to work but. nothing. Have I got another duff one ? Any suggestions as to how to get it to work? I already installed the softwear from Logitechs own site and it can't detect the camera either.... am I doind/ not doing something wrong? I hate to have to send it back again.