iPhone 3G not showing in iTunes Windows 7 x64

I have a continuing problem when trying to get my iPhone to connect to one of my Windows 7 PCs. I have a Acer 6920G with Win7 x64 which works fine, but my desktop, which has the same version of windows and, more importantly, my iTunes library has issues. I have followed the suggestions of reinstalling drivers, iTunes and powering the iPhone off, but to no avail. The computer sees the iPhone and I can access it through explorer but iTunes does not list it. I have iTunes 9 and OS 3.1, with a hope that this would be the solution, but no better. I have tried restarting services too. Any ideas?
PC iPhone OS 3.0.1 Win 7 x64, iPhone )S3.1, iTunes 9