Take all other drives except the DVD player out of the pc. Boot into bios (F2 on start up) and make the dvd player the first boot priority - that's if its Windows on a disk. If its Windows on a usb (downloaded) then make the usb drives the first boot priority. Save changes and exit.
Turn put in the windows disk or usb. Turn off the pv. Start it up again and follow instructions.
When finished, restart the pc into bios again (F2) and reset the boot priority so the hard drive is first. save and exit. shutdown then restart the pc.
All this is on the MS website. Google it.