iPhone 6 plus doesn't appear on iTunes 12.1
I updated my iPhone 6 Plus while iTunes was updating to 12.1 on Windows 8.1 today. After both updates were done, I tried to sync my phone with my computer by both cable & Wi-Fi. But my phone didn't appear on iTunes with neither of them. Everytime I try to sync it with cable, my phone asks whether it should trust the computer or not. I tap on trust, still it doesn't on my iTunes. After a few tries on that, I tried to restart my computer & phone then sync. Even after restarted them, I still get the trust question. On Wi-Fi, nothing is asked. I've twice checked the authorization on both phone & computer, they're both authorized. What should I do?
Sorry I made if I made any grammer mistakes or for not understable sentences. English is not my first language
iPhone 6 Plus, iOS 8.1.3