Under normal circumstances, HD24tools should automatically detect any HD24 drives hooked up to your computer. However, there are a few scenarios in which HD24connect is prevented from doing so. In such cases, the two main questions to ask are, "is there a hardware issue?" and "is there a permissions issue?" I'll go into more detail about these below.
Drive detection can usually be chalked up to a hardware issue if the computer doesn't detect the drive hardware at all. This is different from the computer not showing the drive in the usual manner; Under Windows, for instance, there will never be a drive letter assigned to the drive, and on the Mac the drive will never be mounted by the computer. This however does not mean that the computer doesn't detect the drive hardware.
To find out if the computer detected the drive hardware, we'll need to find out if the computer has assigned a device name to the drive. If so, it has apparently detected the hardware itself. Under section "HD24 Drive recovery" of this manual, you'll find information on how to determine the device name of the HD24 drive for your operating system, be it Windows, Mac or Linux. Whenever you see an "Unknown/Not initialized" drive and you're not also running another operating system such as Linux, then most likely that unknown drive will be the HD24 drive. In such cases, you can probably rule out a hardware issue and it's more likely that any drive detection problems are down to access control permissions.
Assuming your drive detection issue is a hardware problem, there are a few things you can try.
If you're hooking up a drive via USB, try a different USB port- I've had a situation where three out of four USB slots on the back of my computer were occupied and a device detection failed whenever I tried to plug in into the fourth port. When I tried the USB port in the front of my PC, things worked fine. I suppose the collective amount of current being drawn from the USB ports was too much. If you have any USB hub between the drive and your computer, try leaving it out.
I've had a caddy die on me in the past - drives would be recognized in one caddy but not in the other. I've also had a situation where the IDE flat cable didn't quite fit well into the drive. You've tried two different enclosures, so the odds that your problems are something like this are pretty slim.
Have you ruled out the possibility that your USB cable may have gone bad? Do you have the possibility to connect the drive straight to the motherboard with an IDE flatcable?
If using a USB smart cable, have you made sure to also provide the drive with power from a power supply?
Finally, some drive detection issues have been observed to be related to drives drawing a lot of power during spin-up. Yahoo group member Walter H. determined that his Barracuda drive drew 2A during about 20 seconds on spin up, causing detection to fail on his computer. He solved his detection issues with a relatively simple power supply hack.
Once you've ruled out hardware issues (by establishing that your drive is being detected by the computer), there still may be a permissions issue restricting HD24tools from gaining sector-level access to the drive.
Back in the XP days, every program had "raw" sector-level access to drives, which allowed malicious software to corrupt drives. From Vista on Microsoft has wised up and hardened the security of Windows. That's a good thing, but it does mean that HD24tools can't do its normal business unless explicitly granted permission to do so. This is the reason why it needs to be "Run as Administrator" as described on this page:
http://ringbreak.dnd.utwente.nl/~mrjb/hd24tools/hd24tools_windows7.html
It should be possible to work around most drive permission issues on any of the supported operating systems by running HD24tools as Administrator, root or superuser. If HD24tools fails to detect any drives as "normal" user but as administrator/root/superuser it works just fine, this shows that the "normal" user hasn't been granted sector level read/write access. Although it's possible to run HD24tools as superuser, it's not considered good practice. (Note that under Windows, as of yet, there doesn't seem to be another way. If you find one, I'd be thrilled to include it here)
Once you've established there's a permission issue by running HD24tools as superuser, you should normally (on Mac and Linux) be able to set drive device read/write permissions to be available to regular users. The procedure is similar between Mac and Linux.
Once you've found the HD24 device name, start up a terminal. Let's assume the HD24 device name is /dev/drivehd24, then in the terminal you would type
chmod +r /dev/drivehd24
followed by enter. Note all the spaces, direction of the slashes etc. This should enable read permissions on the drive for all users. Note that this command needs to be run as root; this can either be done by prefixing it with "sudo" like so:
sudo chmod +r /dev/drivehd24
or by switching to superuser first like so:
sudo su
followed by the above chmod statement. In both cases, you'll need to enter the sudo password (which should normally be the same as your user password).
If you wish to write back to HD24 drives, you'll need to enable write permissions, type
chmod +w /dev/drivehd24
(once again, you'll either need to be root or prefix this with sudo ; also, once again the above is assuming it is /dev/drivehd24 that's your HD24 drive).
You can also revoke permissions with chmod -r and chmod -w but you may end up revoking permissions to yourself!
Instead of +r +w -r -w it's probably best to use fixed permissions:
chmod 600 /dev/drivehd24
Read+write for root, nothing for either operator or others
chmod 640 /dev/drivehd24
Read+write for root, read for operator, non for others
chmod 644 /dev/drivehd24
Read+write for root, read for operator, read for others
Under various Linux distributions, instead of doing the above it's best to add your user to the "disk" group, making sure that that group has the correct drive permissions.
Since this is a relatively new manual page, it might be all the above still requires a bit of finetuning to make it easier to work with. If after reading all of the above you still have questions or trouble getting things to work, drop me a note and we'll work from there.