USB to serial port requires a driver. You need to check whether your driver is installed. Then check whether your USB to serial port cable is good. Then continue with the next steps.

1. First of all, you should check whether there is a problem with the minimum system of the board you are welding. The minimum system includes whether the single chip microcomputer is broken, whether the crystal oscillator and reset resistance are connected well, and whether the two capacitors are welded well. If everything is OK, go to step 2.

Confirm whether the COM port of the computer corresponds to the COM port of the computer, and then whether there is a problem with the connection of the line out of the serial port: the "receiving" of the computer is connected to the "sending" of the single chip microcomputer, the "sending" of the computer com is connected to the "receiving" of the single chip microcomputer, and the "ground" of the computer is connected to the "ground" of the single chip microcomputer.

Check the level conversion IC MAX232 to see if the level conversion IC is broken. If all the above is normal, it depends on whether the power supply of the single chip microcomputer is normal. It depends on whether your single chip microcomputer is powered by 5V or how much. If everything is normal, it should be able to burn in.