Apple Power Mac G3 beige desktop - HDD advice [SOLVED]

Hi,
I recently got a Power Mac G3 cheap but it's missing the hard drive.
I found a really old 20MB IDE replacement out of an old PC. The Power Mac recognises it and so I partitioned it, formatted and installed the OS (OS 9 if I recall). Unfortunately on reboot the hard drive isn't detected. If I reboot with the CD I'm still not able to mount/access the HDD without starting again by formatting.
Can anyone advise what I'm doing wrong here?
Cheers
I recently got a Power Mac G3 cheap but it's missing the hard drive.
I found a really old 20MB IDE replacement out of an old PC. The Power Mac recognises it and so I partitioned it, formatted and installed the OS (OS 9 if I recall). Unfortunately on reboot the hard drive isn't detected. If I reboot with the CD I'm still not able to mount/access the HDD without starting again by formatting.
Can anyone advise what I'm doing wrong here?
Cheers