Try the following:
1- Make sure you have the latest version of iTunes installed on your laptop, then back-up your phone to your laptop;
2- Turn off "Find My iPhone" on your iPhone (Settings>iCloud>Find-My-iPhone>Off);
3- Turn off "Sim Pin"on your iPhone (Settings>Phone>Sim-Pin>Off);
4- Access DFU mode: press & hold your (Home Button + Power Button) together for 12 seconds, then release only your (Power Button), and keep pressing the (Home Button) for another 15 seconds,
5- Connect your iPhone to your laptop, and turn on iTunes in case iTunes doesn't start automatically,
6- iTunes will say it detected a phone in restore mode. If not, try repeating step 4 (accessing DFU mode),
7- You will be prompted to download and restore the latest version of iOS, accept this option and let you laptop download iOS 8.1.2 which will be automatically installed on you phone. Do not disconnect until the process is finished.
8- You can now restore the latest back-up to recover your data.
Let us know if the above helped solve your issue.