I mistakenly connected GND of the LCD L298 with VCC of Arduino Board. The LCD stops showing the previous boxes but the green background is still on. I wonder if it has broken or not because when I wanted to print words on it, it didn't work
The what?
Code and schematic, please.
I just connect LCD to Arrduino to turn it on and then it made a bip sound , no code actually. But instead of GND-negative,VCC-positive I did the opposite. I am still learning so no code or the like. Thank you
I've never heard of a LCD making a sound.
It was a LCD with I2C.
Why do you need urgent help, is LCD on fire?
Oh yeah, first time using Forum, it obliged me to make a title. Running my eyes around and I got here title. Sorry if it was not worth your time. Next time, I will be more careful. By the way, I don't know that Arduino community is this 'tough'.
I've never heard of an I2C LCD making a noise either.
Feel free to join in with details and observations
It screams in agony before it dies when you reverse polarity
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Hi @happylifw
Is your LCD's I2C removable?
Post a photo of your LCD also showing the I2C.
Hi
It looks like the I2C is not removable.
If you have experience with soldering, try removing the I2C, and connecting only LCD pins 1 and 2,
( 1 = Gnd 2 = +5V) and see if squares appear in the top row.
But if you don't have experience with soldering, I suggest purchasing a new LCD.
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Thank you so much
Have you tried an I2C scanner?
Holly No. So it can figure out whether I2C has broken or not, right? I will try it. Love you!
You do have pullups on the I2C lines?
What value?
I would recommend installing the hd44780 library. You can install it directly from the IDE GUI using the library manager.
It has support for this type of device.
It also includes a diagnostic sketch, I2CexpDiag, that can probe and examine the device to see if it is working and report any issues it finds on the serial monitor in the IDE.
You can find the diagnostic sketch and all the examples under the hd44780_I2Cexp i/o class.
Here is a link to the github page where you if scroll down, you can find additional information on the library including detailed instructions for how to install the library.
Here is a direct link to the installation instructions:
Here is a link to the wiki for hd44780_I2Cexp i/o class:
Run the diag sketch and report back what it prints out.
--- bill
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So you did see the "blocks" on the first row previously?
OK, if you connect power only to the display which did show the "blocks" previously and it now does not show the blocks, then the HD44780 (or clone thereof) chip is in fact, dead. 
In order to show the "blocks", the contrast potentiometer must be set. If it was set before the mishap and did show the blocks, and has not been changed since, then the display would show the blocks with only the (correct, same 5 V) power connected. Showing the blocks indicates that the contrast is set but the HD44780 has not been initialised which is to say it is operating but has not responded to your code.
There is most likely no point removing the I²C "backpack" as a test as without the contrast potentiometer, the display will not operate anyway. If you have blown the HD44780, then you have probably blown the PCF8574 on the "backpack" and it is not worth salvage. 
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