My Iphone 4 is in recovery mode and is connected to Itunes to recover but after days of connection the process bar stops. Does not finish the process.

I was unable to make phone calls with my Iphone 4, all other functions operated ok, [I could recieve calls, messages, etc] I decided to restore my phone using Itunes however after days of having my phone connected to my windows computer using Itunes, the process bar reaches a certain point and stops. Can anyone suggest a solution?