What specifically does the device and/or iTunes do when you have it plugged in? You say it connects... does that mean you can access it's menu in iTunes?
Try rebooting the device while it's unplugged, reboot your computer and then connect your iPhone again to see if the problem persists. Let me know if this helped.
When I connect my iphone 4 to my Mac it charges and connects to itunes but I can't delete or add songs, and I can't sync anything.