Besides everything oldturkey03 said. Try using a different usb cord. Try uninstalling all Apple applications on your computer. Then reinstalling them. Also there are several nonApple applications that enjoy a good reputation for resolving the problem you discuss (iREB & iRecovery). Here are some links to find these applications and instructions on how to use them.
[http://www.ihackintosh.com/2009/07/irecovery-iphone-recovery-mode-loop-restart/]
[http://www.iphoneheat.com/2010/02/how-to-fix-iphone-recovery-mode-loop/]