iPhone 4 iTunes restore error

I have an iPhone 4 for like 3 months now. I had a few problems, but nothing important and my friend advised me to jailbreak it and resolve the problems this way. So I tried it but it was useless for me since i dont know anything about this stuff and I wanted to restore it completely to new software using iTunes, but it just keeps getting error 30xx (number slightly above 3000, dont remember exactly) and i tried to fix it, but it didnt work, so i tried another pc, but the same error occured, do you think this error is because of jalbroken device or is it just bad luck?

edit 1 - more info - so i tried connecting in DFU mode --> error 3014, tried another pc, still the same error

My OS version is 7.1.2, i tried it on windows 7 and 8.1

I tried the HOST file fix but still the error keeps occuring. Could downgrading (and then upgrading) software help?