Proximity sensor, hard reset

Hello I've been reading a few threads on here with regards changing the LCD/digitizer people are having problems with the prox sensor. It doesn't sense at all, I'm thinking it must be a software issue as the screen that I put on was a genuine apple screen from another phone. I read on another thread that if you do hard reset it can solve your problem. I tried resetting it from the handset itself, it didn't work. My question is, what is meant by a hard reset? One where you connect to iTunes etc. thanks for any help given. Regards Matthew