I’m talking about IDE (in contrast to SATA, which we’re not using, yet) disks which have been prepared with the new lubuntu image. However, parts 1 to 4 and 7 apply to any IDE disk in any computer. Part 5 applies to any system booting with grub, which is basically anything linux-like. Part 6 applies to all ubuntu-like systems.

1. Always check if the disk is correctly jumpered before putting it in. It should be jumpered to “master” or “single” if you’re doing the standard setup. Usually there is a little guide written somewhere on the disk itself or the jumper positions are labeled. Don’t randomly try different positions, but understand how it’s supposed to be done instead. Most of the time it’s very obvious.
2. Never leave the end connector of the IDE data cable (the big flat thing with the 40-pin female connectors) unused. Doing that creates unfortunate electrical conditions and may lead to the disk not being recognized. It’s recommended that you put only one device on each data IDE cable and use the end connector for that, leaving the middle connector unused. If you don’t have enough cables or headers on the mainboard to connect all disks and CD drives like this you may put an additional drive on the middle connector. Be careful to jumper the one on the middle connector as slave and the one on the end connector as master then. Mind that this reduces throughput on both drives. Mind also that installing multiple hard disks may mess up the hard disk enumeration by the operating system and/or BIOS, possibly preventing the system from booting correctly.
3. If you boot with the disk and the BIOS comes up with some “disk not recognized”, “press F1 to resume” or similar, you may have to enter the BIOS setup once, have the disk detected and save the settings. This is different on every computer, but generally you get into the BIOS setup by pressing del or F2 on booting. Most of the time, however, if the BIOS doesn’t recognize the disk right away either the disk is broken or the BIOS doesn’t like it. Just try with a different disk.
4. If the computer seems to hate any disk you install, it may be related to corrupt BIOS settings. I’ll quote Help & Troubleshooting here:
   

   known BIOS issue on Dell Desktop computers: BIOS doesn’t recognize HD and/or CD-ROM Reader
   BIOS output:
   “BIOS “Primary Drive 0 …. Unknown device.” …. “Secondary Drive 0 …. Unknown device.”
   Avoid BIOS updates, situation is likely going worse.
   try: shutting down the computer, remove power cable. wait for a minute. take battery of motherboard out. wait/clean > contacts/ proof cable connections/ put battery back in. BIOS should recognize the hard drive
   further things proposed:
   - 2 end IDE cable, the plug in the end should go into master, the one in the middle into a slave
   - clear the CMOS via jumpers instead
   

5. If the grub screen with the different boot modes (normal, “rescue”, memtest86+) shows up, just press enter. The rescue mode is not very useful for inexperienced users. The grub screen should not actually show up but in some situations it still does. I haven’t found out why. In any case, if the grub screen shows up, you know that you’ve jumpered the disk correctly, it is recognized by the BIOS and the computer can load data from it. After all, grub is loaded from disk. Most likely you don’t want to change the disk anymore now.
6. If the blue “Lubuntu” screen with the blinking dots asks you if it should repair the hard disk, let it. I think you have to press “r” at that point, but I’m not sure. 99% of the time the disk is not actually broken at that point but for some reason or another the OS still thinks it has to be repaired. That only happens on the first boot with the new disk and I haven’t figured out why, yet. Usually it will successfully repair the disk and then boot normally.
7. As a general recommendation: Try to keep the computer open until you’ve made sure the disk is OK and will work in this computer. It will save you a lot of time normally spent with opening and closing cases. Computers generally work fine with an open case. Just be careful with all the cables. I know there are some brain dead case designs which prevent you from starting the computer while the case is open, but those are the exception. In many cases you can even leave the disk outside the case and just connect the power and data cables from the open case to just quickly boot and test if everything is OK.