I have a 24" aoc 2436Vh display and a new 15"

https://everymac.com/systems/apple/macbook_pro/macbook-pro-retina-display-faq/

Having trouble with your HDMI port not detecting your monitors or TVs all of a sudden? Go to system preferences -- Click Display - Hold down the alt option key -- click the newly revealed Detect Displays button on the bottom right of the Display settings panel. That should solve 90% to 99% of issues if your cables and Macbook pro are good. This happens to me all the time when I try to plugin to a 4K tv at the office which is the exact same model I have at home. The one at home works while the one at the office never auto detects. If this did not fix your issue, check that your Macbook Pro HDMI port and HDMI cable ends are clean and free from debri and not damaged, double check that your HDMI cable is working on other devices, make sure your TV or display is powered ON, check that your HDMI cable is securely and fully seated, check that you're on the right input on your TV or Display, make sure the cable is not too long because HDMI has length limits depending on the cable and devices, and then force detect display again on your Macbook pro. If this still did not work, when it worked before. It's likely that your Macbook Pro, TV, or Macbook Pro HDMI port is acting up. I'd recommend taking in your Macbook Pro to the Apple store at that point to get diagnosed. Hope this helped

Most HDTV's have more than one HDMI ports. Move the cable to another port or use the setup button on the side of the HDTV and go the "input" and select a different HDMI port.

It may have something to do with the settings under audio output devices. See if you have options, and ensure that the headphone jack (I assume that's what you're using) is set as the default sound device.

I had this problem with windows using HDMI. try letting the mac boot up all the way before inserting the HDMI.

if this helps please take time to rate

Had the same problem! Solve it: go to the AMD catalist and choose advanced look. then inside the digital display setting you'll see scalling option that will show 10% . Set it to 0%. Done!

MiniDisplay will probabely not support the Cinema's screen resolution...

Hey, you would need a Mini display to HDMI cable and unfortunately the sound cannot be ported through the mini display port.

Unfortunately, the 24" AOC 2436Vw Monitor does not have built in Stereo Speakers. I know that is not the best answer to hear, but after doing a little more research, I found that the 24" AOC 2436Vh Monitor has 2 built 1.5W Stereo Speakers for just $50 more.

You may need a certain connection (MiniDisplay Port to DVI, or MiniDisplay Port to VGA). If you're connecting to an HDMI-compatible projector, you'll need an adapter. You'll also need an adapter if connecting your MDP (MiniDisplay Port) to a DVI or VGA port. Here are some helpful links:
#1 MDP Adapter Video (YouTube)
#2 MDP to HDMI Adapter (RadioShack)
#3 MDP to VGA Adapter (Apple Store)
#4 MDP to DVI Adapter (Apple Store)

http://www.radioshack.com/product/index.jsp?productId=3898890&CAWELAID=447271885

http://store.apple.com/us/product/MB572Z/A

http://store.apple.com/us/product/MB570Z/A