Ok, this is starting to sound like the disk is installed but the partition is not bootable for whatever reason.
If you boot with both mouse buttons held down and get the early startup screen, do you see the hard disk partition in the list of bootable drives?
If it is not bootable, something went wrong before or during the install, but it should be fixable.
Having booted from floppy, can you find the HDToolbox program? It should hopefully be under the Tools directory on your hard disk.
It has been a long time since I saw OS3.1's HDToolbox program, but you should be able to select whichever partition you installed the OS on.
You need to check that it has been made bootable (there is a checkbox somewhere) and that the filesystem is supported. If it is anything other than FFS, you might have a problem. The fact that you can see it when booting from a floppy tends to suggest it isn't the filesystem, unless the floppy has had the filesystem installed on it.
Assuming it is FFS and the partition is not checked as bootable, all you should need to do is tick the bootable checkbox, save the changes to the drive and reboot.
