I know this may sound silly…but have you tried more than one USB cable? I have had issues in the past with cables that worked fine for a while and then just didn’t work. Sometimes they will connect and show up in device manager but not communicate.
Also, the above post is correct. Get your self a Pixhawk. I moved from the apm to Pixhawk. I have a radiolink. They are a much better FC, have a better processor and can compute faster and have much more headroom than an apm running at almost full capacity all the time.