Hard drive ful capacity no recognized

I have a Compaq Presario 7478 with Win98 and a 30 G. hard drive. I just add a new 120 G. hard drive but it only recognize around 24 G. I want know what can I do to make the computer recognize the new disk full capacity?
If it is posible to solve the problem without BIOS flash it would be very nice.
Thank you.