Boot up

I am trying to make one good computer with some used parts I have, mainly a hard drive. It booted up ok, I got as far as it asking me for a 98 boot disk which I put in the A drive. It seemed to go into DOS and an “A” prompt showed. I typed in C:\
then that showed. I didn’t know what to do next.
Now I get on the top left corner of the screen “Press any key to Reboot”. It does this over and over. HELP. In SETUP I put the used hard drive in AUTO.