If you are having issue; being seen Ur iPhone in my computer but not in iTunes, (iPhone 5s-7.1.2 in windows 8,also can be helpful for other versions of windows and iPhones),:then u try these following steps:
1)go to control panel then uninstall APPLE MOBILE DEVICE SUPPORT
2) then open iTunes and try to plug in Ur iPhone
(during this process, appears a dialog screen stating to install different version of ITUNES like 64 bit or 32 bit)
by this time,u will already configure your issue and know what to do
3) So you uninstall Ur current version of iTunes, restart Ur PC and download a fresh copy of required bit iTunes(not by using APPLE SOFTWARE UPDATE)
4)after this u are ready to go,install iTunes, plug in Ur iPhone( don't panic if Ur iPhone is not shown in iTunes), unlock Ur phone and hit the TRUST button
5)enjoying synchronising Ur iPhone iniTunes.
have fun..!