I am not sure this is you problem, but on my previous PC the use of an usb-serial converter in combination with certain other applications (especially audio and video) could cause my PC to hang and often reboot. This did not happen when I used the same gadget and application with the real (hardware) serial port. I never found out what the cause was, I just learned to avoid watching video during intensive USB serial port use. AFAIR this happended with both FTDI and prolific converters. It could have been a SW problem (windows version, USB stack) or maybe hardware (flaky motherboard). With my new PC (different windows version) I have never encountered this problem.

I am not sure this is you problem, but on my previous PC the use of an usb-serial converter in combination with certain other applications (especially audio and video) could cause my PC to hang and often reboot. This did not happen when I used the same gadget and application with the real (hardware) serial port. I never found out what the cause was, I just learned to avoid watching video during intensive USB serial port use. AFAIR this happended with both FTDI and prolific converters. It could have been a SW problem (windows version, USB stack) or maybe hardware (flaky motherboard). With my new PC (different windows version) I have never encountered this problem. (Which is all the better since it does not have a hardware serial port.)