my phone no servicein my house and message states unable to join my wireless network

I just got this replacement phone 30 days ago. After about 3 weeks I would occasionally get a message that said phone was to hot and had to cool down even though it was sitting in my den. As suggested online I reset it. Worked fine about 5 days. Then when turned on ios-6 appeared and different languages scrolled through and said emergency call only. Now when I turn on says no servive and unable to jion my network.