I try to update my iphone 5S to iOS7.1 from a PC. The software update was downloaded and in the process of installing the update the internet connection was was disconnected for unknown reason. My phone's screen show an iTune symbol. I cannot use my phone any more. I want to know what happenep to my iphone. Can I use my phone again?
Hopefully you did a backup before updating? Right? ;-)
If you have a backup file you simply plugin the iPhone to your computer and follow the last step in this guide ("Restore from a backup").
If you didn't make a backup, try to put your iPhone in DFU mode (guide here) and follow the iTunes instructions to restore the iPhone to default. (You will lose your stuff if you haven't backed it up earlier)