Hello, I'm in the following situation:We just bought a new computer (AMD Sempron, 3100 series I thought) and let the two hard disks we had in the old one, be put into the new one. Now, by mistake the first hard disk was inserted as the second one and the second one was inserted as the first one; as I now think of it it had all taken a lot less effort to get things working just by swapping them back, but none of us here feels really comfortable touching the real hardware in there :-/
Probably not what you want to hear, but the right answer is to switch the drives around. As you have found, there are various little tricks and tweaks to try and sort this out by software, but one day you'll come up against something that can't be. You might as well fix it now.
There may be more of a problem than you think: presumably the two hard drives are on one data cable? hda and hdb are the two devices on the first IDE cable, and hdc and hdd are on the second cable. If the drives are hda and hdb then they didn't just have the cables put in the wrong sockets. hda and hdb are distinguished by one being master and the other slave. This is normally set by jumpers on the drives themselves. It is unlikely that you changed the jumpers when you moved the drives to the new computer. If you did, change them back and that is the end of it.
The other possibility is that the jumpers were never set correctly. Probably the drives were not originally bought at the same time, one is likely to have been added later. Some drives have separate master, slave and single jumper settings (also cable select, but this is unlikely to be involved). Some have the single drive setting the same as master, some the same as slave, often one setting is with no jumper (or hanging on one pin only in case you need it later).
If the jumpers aren't right, sometimes things work, but possibly not reliably. I made this mistake recently, and the result was that my second drive would be recognised after a warm boot, but not on power-up. It's quite possible that the drives could be recognised one way round in one machine, and the other way in another.
You probably need to pull out the drives (the jumper details are usually on the case, and you can't read it while the drive is mounted), though if you can read the model number from software you may find the details on the Internet. You might even have a small leaflet that came with the drive. You need to know which is which (probably the smaller capacity drive is the older, and used to be hda) and set the jumpers so that the original hda is master. It's worth copying the jumper details to a sticky label inside the computer case, so you don't have to pull out the drives if you need this information again.
-- Joe