iPhone 3GS stopped syncing with iTunes

[AussieCol]

I have an iPhone 3GS which was used with a PC to sync with MS Outlook via iTunes. I recently bought an Imac 27" i7 to replace my Windows PC (yes, Win7 left me cold too) and the iPhone was connected to the iMac, detected and set up to sync with Entourage through iTunes. I have the latest OS and iTunes versions and my phone is also fully updated. All worked fine until 2 days ago when iTunes stopped detecting the iPhone. The iPhone is recognised in iPhoto and I have reinstalled iTunes 10 as well as following numerous web tips from "experts" but still no detection. Apple just want to sell me an Apple Care agreement (iPhone is just 7 months old) and while the iMac support team have been great, they won't go into in-depth iPhone support. Can anyone assist please?