MS-DOS issue

We turned my old computer on one day (Windows98SE,Pentuim II) and I had the old version of Norton in it so I told my boyfriend to delete it and he deleted it from the start menu. It froze up and when he shut it down it came to the blue screen and wouldn't go any further. He tried anothe hard drive and mother board. He tried to install Windows 98Se back in but it keeps coming up that it won't boot and that we need to insert the system boot disk but we don't have won't. It seems that ms-dos is missing. Is there anyway to get ms-dos back in so that the windows disk will load?