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Ashik, Mac Technician
Category: Mac
Satisfied Customers: 9768
Experience:  Bachelor of Computer Application (BCA), 9+ Years of Experience in troubleshooting Macs, iPhone, iPad, iPod etc
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Problems with LG LED 42" TV and Mac Mini

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Hello, I have an LG LED 42" TV and I am trying to set it up as a monitor for my Mac Mini running Mac OS Lion. Somehow I changed the resolution on the screen preferences window and now I get an "Invalid Format" on the LG TV. I've tried rebooting in safe mode and changing the resolution and that works, but as soon as I boot in normal mode I get the Invalid Format message. What can I do?

Hi and Welcome. My Name is XXXXX XXXXX I look forward to assisting you today with your question.

Before we start, please remember these things. It may take more than one step/answer to solve a problem. So If my answers didn’t work or if you are not satisfied, please don’t Rate my answer as Bad or Poor Service, but please Reply back to me by clicking the “Continue Conversation” or “Reply” button and I will gladly continue to help. Remember, you are rating my Service to you and Not the Outcome of the answer or this website.

Change the resolution to a lower resolution from Safe Mode (not to the default one). Then turn off your Mac and reset the PRAM and NVRAM. Follow the steps below to reset the PRAM and NVRAM

  1. Shut down your Mac
  2. Locate the following keys on the keyboard: Command(Apple), Option, P, and R.
  3. Turn on the computer.
  4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears and before the chime sound.
  5. Hold the keys down until the computer restarts and you hear the startup sound for three times.
  6. Release the keys.

Then restart your Mac in Safe Mode again and change it to another resolution (to a one above the lower). Then restart your Mac (not to Safe Mode) and then change the resolution to a anything below to the highest resolution. Again, restart and then change to the highest resolution or to your preferred one.

Please let me know if that didn't work, so we can continue troubleshooting. Don't Rate my answer until you are satisfied.

Customer: replied 3 years ago.

I tried it but i only heard two start up sounds instead of three. Should i try it again? i must say it is a hard key combination to hold with only one hand

Two startup sound is OK. Your PRAM and NVRAM is reset. Now try the remaining steps.
Customer: replied 3 years ago.

I just finished start up in normal mode and I get the invalid format again.

I will try it again from the beginning


Ok..If that didn't work, we can reset the System Preferences settings to default.Boot into Safe Mode again, on finder, Hold down Option key on your Keyboard, click on Go menu in the top and select Library. This will take you to the Library folder of your User Account. Open Preferences folder.

Trash the file "" from there. Restart your Mac. Let me know if that didn't work
Also, Goto Macinosh HD > Library > Preferences > SystemConfiguration folder and trash this file too : preferences.plist

Then restart.
Customer: replied 3 years ago.

ok, i will delete this one too.

Let me know how it goes.
Customer: replied 3 years ago.

sorry, i was looking for it in the wrong place. I found it and deleted it.

After deleting it, restart in normal mode. Did that work ?
Customer: replied 3 years ago.

I restarted in normal mode but i get the invalid format again


I'm getting out of ideas. Boot into Safe Mode again, goto System Preferences and open Users and Groups. Then create a new administrator account in there. Then restart your Mac and boot into the new administrator account. Does your Mac recognize the monitor ?
Customer: replied 3 years ago.

Ok, I will try it.
But if it doesn't work can we go through your first suggestion step by step? I'd like to give it one more try.

The thing is that earlier today it worked just fine; just that the screen was a little bit off centre so I thought the resolution was incorrect. I tried several options; some worked others gave the invalid format. But after a few seconds the screen came back to the previous resolution. It is just that I don't know when i clicked on the keep settings button and it screwed everything up.

Customer: replied 3 years ago.

OK, so far so good. I logged in to the new Admin user and the TV is recognised.
Now, will this work with the other two previously existing users?

Sure. Unsupported resolutions will really mess up some settings of current account. My first suggestion will confuse your Mac to use default settings, then it allow to change the resolutions to correct one. Lets try again.

Step 1 : Reset the PRAM and NVRAM again (hold down those buttons for 10 seconds)

Step 2 : Restart your Mac in Safe Mode and delete those files I mentioned above

Step 3 : Change the resolution to a working one (select smaller resolution number here)

Step 4 : Restart your Mac to Safe Mode again, select another resolution. Restart into old account. Did that work ?
Ashik and 2 other Mac Specialists are ready to help you
Not sure, try logging into old account. If it still not working, then backup all your files from your old account to a External drive from Safe Mode, login to the new account and copy the files back to your new account from the external drive. The settings of your old account must be messed up.
Customer: replied 3 years ago.

I logged out from the new user and have tried the previous ones.

It works!!!!
I had been breaking my head for almost 3 hours before finding just
Thank you so much.


I'm glad you got it worked and Glad I could help you. Add a bookmark of this page, so you can refer this thread anytime if it happens again or you can get back to me anytime you want through this thread.

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Happy New Year,