Can’t boot from hard drive

I recently installed an extra hard drive into an older machine running windows 2000. When I installed the new hard drive, the computer selected the new drive (also has Win 2000) as the boot drive. I disabled the original hard drive in the device manager and now neither drive will boot. It is telling me that there is no page file on the original hard drive and it will not boot. How can I enable the original hard drive in the device manager when I cannot boot from the hard drive? PLEASE HELP!!