Your iMac Intel 27" EMC 2390 (2010 model) exhibiting a black screen with only the startup sound indicates a failure in either the **GPU, display, or logic board**. Here’s how you can diagnose and potentially fix the issue:
# **1. Check for External Display Output**
- **Connect an external monitor via Mini DisplayPort or Thunderbolt.**
- If the external display works, your internal display or backlight may have failed.
- If nothing appears on the external display, the issue is likely with the GPU or logic board.
# **2. Backlight vs. Display Issue**
- **Shine a flashlight at an angle on the screen** after hearing the startup chime.
- If you faintly see the macOS login screen, the **backlight has failed** (possible LED driver board or power supply issue).
- If you see nothing, the display itself or GPU may be at fault.
# **3. GPU Failure**
- The 2010 iMacs are known for **ATI Radeon GPU failures**.