Not in sync

I've had this error before and it was because the rx pin was accidentally shorted to ground. I've checked it this time and it's not that, and when plugged in the microcontroller gets very hot. The only reason I'm trying to do this is because the program that's on there seems to have stopped working (it was working fine before, I just didn't use it for a while and now this). Any help?

if the micro is getting hot, something is shorted

I've gone over all of the connections and nothing is shorted. I'll try a different cable or something.

Okay, I've gone over every single connection multiple times and it's not any shorting, but it has to be because that's the only answer. The only other thing I can think of is that the program on there is wrong or the bootloader is bad. The LED on pin 13 never lights up when I plug it in and the TX and rx pins both light up, but then there is no transmission during the upload process, the RX led just blinks 3 or 4 times (it changes). Also, if I plug in another power source, the computer won't detect the arduino, although I have done this before for serial monitoring. This makes absolutely no sense anymore and it's starting to bother me. My other arduino nano works perfectly fine.