mobile

So, stuff happened to the phone, the back creaks now and the touch screen is unresponsive sometimes. I want to send it back and I am almost sure they won't repair it for free, but can I send it in with CM12? Or should I flash an ftf and restore my TA?

Also, I just want to ask, how do I restore my TA? In flashmode? In fastboot? While my phone is still on?