How to know whether my iPhone SE 1st gen is dead or not?

Not being able to see what’s going on on the display makes it very difficult to test. The easiest way is to bring the device to an Apple Retail Store or Apple Authorised Service Provider to have them test it. An appointment might be required. Alternatively, there are plenty of phone repair shops that might be able to have a look.

If you want to try something yourself, I have two options below. However, depending on your device settings, the iPhone may refuse to communicate over the Lightning connector until it is unlocked. Unlocking is almost impossible when you can’t see the display.

If you connect the phone to a PC or Mac, you can check if it’s detected as a device. If it’s detected as a device, it might mean the display is not functioning.

Connect the iPhone to the computer and and wait about five minutes. This should give the phone brought time to startup and be ready to talk over USB.

macOS:

• Click the Apple and choose About this Mac.
• Depending on the version of macOS, you’ll have two different ways to view the System Report:
  • Recent macOS: Click More Info, scroll down and choose System Report.
  • Older macOS: Click System Report.
• In the new window click USB on the left column.
• Review the list for something that says iPhone.

Microsoft Windows:

• Click the Windows button.
• In the search box on the taskbar, type Device Manager, then select it from the results.
• Depending on the version of Windows and the drivers installed, you may see the iPhone appear in one of several places:
  • Portable Devices may have Apple iPhone.
  • Other devices may show iPhone.

If the iPhone shows in one of those places, there’s some hope you’ll be able to replace a part to use the device again.

Connect the iPhone to a TV and check if there is any video displayed on the TV. Your best bet is to use an Apple Lightning Digital AV Adapter (https://www.apple.com/shop/product/MD826...). However some third-party adapter may also work.

• Connect a Lightning cable to a USB power adapter and the Lightning AV adapter.
• Connect a HDMI cable to the TV and Lightning AV adapter.
• Turn on the TV and turn to the correct HDMI input.
• Connect the phone to Lightning AV adapter and wait several minutes. If the phone turns on, you should see the Lock Screen appear.

If no video appears, check you are using the correct HDMI input and press the home button to wake the phone if it has gone to sleep.