PC won't boot with second hard drive

[jackn]

I have two hard drives. It's an old Gateway PC.
I'll call one 'old20' and the other 'new40'.
The old20 was sitting in a caddy (a removable rack). The new40 on top of it, in a built-in slot.

Both were installed and in working order. The old20 had the OS. The new40 had data.

I then wanted to switch them.
I moved the old20 to the (removable) caddy, and the new40 to the built-in slot on top. I did the connections to the IDE ribbon (is that what it's called?) as best I could...
In the course of this switch, I also moved the jumper from the old20 to the new40, in order to give the new40 'master' status. The old20 has no jumper now.

The new40 became the disk with operaing systems. I meant for the old20 to become the data storage drive.

The PC works just fine with the new40.
I cannot, however, install the old20 as my data drive.

When I try to install the old20 by plugging in the (removable) caddy, I just get the message 'Hard drive was not found', and the PC just hangs there and won't boot...

Here's what the BIOS says:
IDE1 master - new40 (Maxtor)
IDE1 slave - not installed
IDE2 maser - not installed
IDE2 slave - CDRW (Samsung)

I also had the old20 checked by our SysAdmin at work, and he said the disk was just fine.

Possible leads:
1. The old20 needs a jumper, too, to be considered a slave.
2. Something is wrong about the way the ribbon cables were connected.
3. IDE2 already has a slave, so...

Both the old20 and the new40 were running just fine prior to the switch, so there must be some setup, which I've missed, that allows them to work together.

Help?

Thanks...

Jackn

[street1 (RIP)]

Hello jackn,Welcome to computerhope.

I believe your old20 needs to be jumpered as slave.Do you have an old jumper somewhere,you can use?

I like the "OLD" senario.

[GX1_Man]

If you post the drive make AND model we can peruse the appropriate jumper settings.

If it is not recognized in the BIOS, Windows is irrelevant.

[lsfg]

If you jump into your BIOS set up on boot up by pressing the correct interupt key you may let the Auto find determine if you have set up the master/slave identity correctly.  It should post the two drives on the screen when booting.  Generally a jumper tells both drives their position in the sequence.  You may not have the second one turned on in the CMOS.  You may also be running a larger than 137 gb drive on an old system that can't handle the large format.  Jumper switches can sometimes fix that too.  Be careful when entering the BIOS because settings incorrectly can sometime lock you out from booting altogether.