follow the below steps and you are all set no worries:
1- shutdown your iphone with the hard reset "home button and power for 10 second"
2- connect the usb cable to the pc but not to the iphone"
3- open itunes
4- while the iphone is off, press the home button for 5-10 seconds then plus the other end of the white connection cable into the iphone
5- do not remove your finger from the home button
6- itunes will detect it and you can now restore it
7- finally you need to jailbreak it again..follow the web instructions
good luck
thank you, god damn, thank you!