When you test this drive in your other machine, do you test the drive and ide cable all at once?
In all the previous cases the sandisk moved to the slave device if you had a HD onboard...the HD always defaults to master.
Is the IDE cable upside down?
In the BIOS do you have drive C and D set to AUTO?
Do you have boot sequence C only (sandisk still has image on it right?
It sounds like bad wiring if it disables the sandisk when you plug the HD in...and your bios is set up right.