arduino suddently stops working, then avrdude: stk500_getsync() error appears.

Hello,

I was just running code on my Arduino Uno, powered from a 9v battery. Theonly things connected to arduino were 4 transistor communicatiing with a 12v circuit (protected by 4 diodes) and a i2l display connected to port A5, A4, ground and 3.3V.

While working on the circuit i noticed that the display was turned off. I tried to plug and unplug the battery but still wasn’t working. I suspected that i fried my arduino, but then when i connected it to the PC and tired to upload a sketch, the IDE gave me this error:

avrdude: stk500_getsync(). (and then it retried 10 times without success)

NOW unlikely other people that had a similar problem, i had not uploaded any sketch recently to my arduino (and yes, i checked the port and the arduino model and they were correct). Bootloader got corrupted/deleted maybe? but how? it’s possible it happened just by normally running some code?
Also the arduino board seems fine…it’s not hot in any of the parts…but i still don’t know what could have happened to it, please help :frowning:

Run the loop back tests on your board.

I'd bet $1 you accidentally ran 12v into your board