IPhone – Computer doesn’t detect the iPhone 7

Run Activity Monitor (Applications/Utilities); do you see the iTunes Helper service running? Make sure you set the view to "All processes", not "My Processes". If it's not running, that's your problem. Re-install iTunes and away you go.

Verify that the iPod service is running by doing the following:

First, close iTunes and disconnect your iPhone from your computer. Then:

1. Go to Start

2. Go to Run

3. Type "services.msc" and hit enter.

4. Find the iPod Service

5. Right click on it and click Start or Restart Service

6. Reconnect your iPhone to your machine.

If this does not resolve the issue, try going through the steps in this knowledgebase article.