iPhone 4 and iTunes are neither of them Windows products... and even though you may be interfacing the two through a Windows computer, this is not the best place for help.
Also, when asking there you may want to include more detail...
iPhone 4 and iTunes is sort of generic. What computer OS and version are you using? OS version on your iPhone4? Does it boot? What are you trying to accomplish? Sounds sort of like you need a restore from iTunes??? Provide more detail to get better help and quicker.