Presumably, your computer is hanging shortly after the boot process with an error message regarding the hard drive. On this screen, there should be a message inviting you to enter setup by hitting a certain key (often 'DEL', 'ESC' or one of the function keys. Pressing that will take you to the BIOS setup routine, and in there, there should be an option to set the 'type' of hard drive that's installed. This is likely to be easy to spot, but if not, let us know what sort of BIOS is in place on your system - this is likely to be displayed either in the top left hand corner of the inital screen (a banner displaying the manufacturer such as American Megatrends, Phoenix etc) - or there may be a long line of letters and numbers at the very bottom of the screen; if you can let us know what's on that first screen (where the machine 'freezes'), or better still, upload an image of it, there'll be someone here that will be able to talk you though the process of getting it up and running again (assuming, of course, that the HDD hasn't died).
On a Pentium-based system? I very much doubt it. Every post-486 system I've ever used has had an auto-detect function.
Regards,
M.