So long as you have not tried to write anything to, or use recovery software on the drive, you should be fine.
Start by entering BIOS setup and making sure that the BIOS is set to auto-detect, and that both drives are properly identified.
If the BIOS was set to a specific drive type, it will not recognize a different drive correctly.
Next, double check the jumper settings on BOTH drives.
Make sure that the master drive is jumpered for master with slave present. And the slave drive is jumpered as slave.
Next, try a different IDE cable. You might have a cable select style cable. Or, the IDE cable may have been damaged when you reset the jumpers.
With a cable select style cable, you MUST connect the drives to the specified connectors for master and slave.
What happens when you swap the drives back to the original master / slave settings?
Another thought, did you use the drive manufactures software to set up the Quantum drive when it was first installed?
If so, you might have BIOS / Drive overlay software installed.
Drive overlay software MUST be installed on the boot drive for the software to function.
I have many a time had problems with 2 different manufactures drives as master and slave on the same IDE cable. Some drives just will not function as a slave with a different brand of drive as the master.
Have you tried moving the drive to the secondary IDE cable?
You can disconnect your CD drives temporarily to check out if the drive functions correctly by itself.
Chas