Is the old drive still installed? Have you changed anythng in the bios concerning drive priority? You always need the drive you are installing the OS on be primary, or first in the disk order, unless you are installing a second OS.
If you are not trying to dual boot, I would suggest you remove the old drive, unless you are needing the old OS for an upgrade custom install...
Another thing might be that WD PATA drives do not like being set to master if they are the only drive on the Pata controller. Since you did not say if your old drive was PATA or SATA, I just thought I would mention it.