I will help you to solve your problem, don't worry just follow as I say.
1. Firstly it is not a big problem just do as I say.
2. Connect your device to the PC and then launch the iTunes software.
3. And then go for the option of 'Restore' in that iTunes.
But if your device doesn't respond to it.
4. Then try to update the iTunes software to latest version.
And using windows OS means you need to uninstall the whole previous version of software and need to download and install the latest version of it.
5. And if you are having the third party apps such as Antivirus and etc are installed then it will object your phone to respond to iTunes. So you need to update your iOS software at any cost, which is the only way to