error: avrdude: stk500_getsync(): not in sync: resp=0x00
This is not a very explicit error, I give you that. It could be lots of things, but I think I remember I had this particular error a while back because of bootloader issues. 

The bootloader on most arduinos listens for a few seconds on the USART, checks and copies a code if it receives a correct one or otherwise just gives up, then calls the main program and does not run in the background. Therefore when the uploader tries to communicate with the board, it might be already running the main program and be unresponsive, hence the "not in sync". The simple fix is to hit "upload", wait for the program to compile, and reset the board just when the program starts being uploaded. There must be a second leeway, but it has always solved the problem. 

I think I remember it's also possible to upload a code compiled for another board, which prevents proper synchronisation once the wrong code is uploaded. Not sure under which conditions this can happen (probably when the bootloader is uploaded and run together with the main program as one single program), but that would be worth investigating if none of that works. 

Last resort, I'd buy a programmer (it's a good investment) and upload a fresh bootloader+blink program. 

Either way, I'd look at the bootloader code of your platform online. Not only there might be the answer to your problem, but you'll also find the baudrate you're supposed to talk to the board with (19200 in the newest versions, it seems). If you never tempered with the bootloader, it should be the stock one.

Without external components connected to force short circuits on the outputs etc. it is virtually impossible to break a board by experience.