Hi MattyBdog,
This article:
http://support.apple.com/kb/HT1207 provides more information about the disk cannot be found errors along with some tips.
Is the PC a desktop or laptop? What security software is running on it?
Make sure the iPhone is directly connected to the PC not connected to a hub, keyboard or monitor. Make sure its connected using the cable that came with the iPhone. Also, try disconnecting any other USB devices directly connected to the PC.
-Jason