Please say which operating system, you are using.
If you're using Windows, usually the problem is your USB cable uses a counterfeit chip and Windows automatically upgrades the driver which then will no longer work for counterfeit chips. Check "Device Manager" to see if you have unrecognized USB serial port devices, if you do "roll back the driver" and it should work at least temporarily. (Cure is to buy a USB to serial port device with FTDI chip set like this one:
https://smile.amazon.com/dp/B00HUB0ONK/)