can't update my itunes software with windows 8.1

I try to install itunes version 11.1.5 as prompted and errors occur. I have downloaded and tried to install manually as instructed. No go. Says another installation is in progress. Not! Restarted tried again...no go. Any advice??? I am trying to get itunes to recognize my iphone and ipod touch. itunes won't recognize in order to sync. VERY frustrated.