I had this situation with my L710 went to mobile shop to fix it. They asked for $50 but at the end they messed up with my phone, broke proximity sensor, buttons were "fallen down". went there few times and finally my phone completely died (I think it was screen) Ended up buying new phone from them, of course for less price.. So, if you got warranty you better use that I think. Or you could try replace it yourself (find tutorial video on YouTube)