Which flavour of SliTaz did you download? The slitaz-base-iso version only installs the bare minimum of stuff and is only command line based. You can install SliTaz with the slitaz-installer command with that version.

If you have the full 30MB liveCD, then it means something isn't starting as it should. This could be anything from xorg to openbox not starting. Do you get any errors while it's booting? Type dmesg and look for any errors from the command line and tell us about it here.

I did download the 30MB ISO. It gives me the following message if I type in "dmesg": "Buffer I/O error on device, dev hda, logical block 7755" with a long explenation.

From what I read about this kind of error with other distros, this error normally gets caused either by a faulty CD. So try redownloading the iso and see if that helps.

This can also be caused by a error in HAL's detection and setup of the drive in question. This means a misconfigured fstab which generally would mean that you couldn't use the drive. If it was the main HDD, then it causes some issues, but SliTaz would still boot into it's Desktop enviroment then. Maybe hda is your CD/DVD ROM? It's strange because it does dumb you into command line. If it wasn't detecting the drive at all, then it wouldn't even get this far.

That leaves the third, and less likely one, of a faulty HDD with errors on it or just a file systems that SliTaz can't handle. If you can use this drive with other distros, then this is unlikely the case here.