During copying files even small size (Say about 500 MB), Windows 10 suddenly drops speed after about 30 seconds to 10 KBPS and then many times to Zero. This transfer process thus becomes extremely slow and along with that the whole laptop becomes extremely slow – Example during transfer to open My Computer takes 3 minutes to open and finally the PC hangs. If no data transfer is happening the laptop works perfect but only after reboot. Once data transfer has started the whole PC slows down and works normally only after reboot.
did you check for virus. if possible try doing a clean install.