I have a 20 GB Quantum Fireball HD that I tested not to long ago(a month?). I told my friend he could have it for a bit of extra space, and that I would put a couple of things on it for him. So, I plugged it into my free IDE ending on my only ribbon. It shows up in the loading screen run by my BIOS. It does not show up in Windows however. Any ideas? All help is much appreciated. Thank you.

Perhaps you have a privacy setting turned on that you shouldn't have?

It is sometime occurred when you run your HDD after long time.
For that you have to start PC in safe mode.

IF not done than run Disk check with CHKDSK in startup.
Otherwise you have to take with repair shop for some small maintenance.

I will run CHKDSK and look at my settings. Thanks for the suggestions, and I will post the result.

Ok, so I looked around and I can't seem to find CHKDSK anywhere. From startup anyway. I was able to sort of run it in Windows Powershell, but that didn't get me anywhere. I also looked at my settings that seemed related to this subject. I found nothing to change that would fix it. So I'm still stuck.

Try Control panel choose administrative tools choose computer management choose disk management and see if it appears there. You can also do quite a bit with there.

I went into disk management and it didn't show up there. Anything else?

If it does not show up in disk management then windows does not see it but you say that it shows in the BIOS? I would suggest you check the cable connection ( may not be making proper contact or reversed ).

I plugged them in properly. I can't reverse the IDE or Mollux cords because of the way they are shaped. And I made sure to plug them in all the way, and that they weren't loose.

Just naming out solutions here possibly:

Are you sure that you have the power cable plugged in?
Maybe one of your pins is missing or broken on your hard drive?
Is your hard drive set to the right setting (master,slave, etc.)?
Maybe the connector on your IDE cable is bad?

What is the size of your main hdd?

1 You could try starting your pc with a windows set up disk, if it sees your 20Gig hdd, re-partion it, start windows normally and see it appears in the disk management.

2 Failing that, download the manufacturers software and run it.

3 You might also try connecting it to via you secondary ide port.

I have seen this before, its unfortunately dead, what happened is that the motor died. The bios can still see it because it only needs to see the chip on the hd to get an id, the hd doesnt need to spool up. Windows on the other hand needs to have the hdd spinning to id it.

Have you checked the jumpers? Make sure its set properly, and if set to cable select make sure you have a cable select cable. If not, set Master/Slave on both drives.