1. Check the Charge
One of the most basic but essential things to do when your iPhone won’t turn on is to check if it’s just out of battery or not. Connect your iPhone to the charger and let it charge for a few minutes, and then try turning it on again. If it still doesn’t turn on, continue to check other things.

2. Check the Connection
Sometimes, the charging port or the lightning cable isn’t always consistent, leading to an erratic or faulty connection. Try switching out different lightning cables or connect the current one to another power source, like a computer, and see if it makes a difference. If it does, then your problem is likely have a charging port issue.

3. Restart your iPhone
If your iPhone’s battery is not dead, and you’ve checked the charger and cable connections, then the next step is to restart it. Press and hold down the power button and home button at the same time until the Apple logo appears (the length of time it takes to restart varies from phone model to model).

4. Use iTunes
Another option is to try and connect your iPhone to iTunes on your computer to see if there’s any problem with the operating system. Keep your iPhone connected to your computer and open iTunes. If an update is available, then prompt it to download and install, and then restart the iPhone again.

5. Boot in DFU Mode
DFU (Device Firmware Update) mode is an emergency mode that allows you to restore the iPhone to its original state if all other options have failed. It’s a more potent variation of recovery mode that works on older versions of iOS. Firstly, connect your iPhone to a computer and launch iTunes. Press and hold the Home button and hold the power button simultaneously. After approximately eight seconds, release the power button but keep holding home until iTunes pops up with “iTunes has detected an iPhone in recovery mode.”

6. Contact Apple
If after trying all these options, it’s still not working, then it’s time to contact Apple directly to handle the problem.

In conclusion, fixing an iPhone that won’t turn on can be a bit tricky, but trying the above steps should help you fix the problem. Always ensure that you’re not doing anything without knowing what you’re doing, and everything should be fine.