compaq 5304 Hd upgrade HELP

Hi I have a compaq presario 5304 & installed a 20 gig HD as well as a 2nd HD (13 gig) slave
The HD installed when purchased was a 4gig and when I upgraded to the 20 gig the tech at future shop had to do something in order to read the bigger drive. My problem now is that I've since reformatted the 20 gig but it only reads 4 gig is available but the system info says 19 + gig and recognises the 2nd drive. Any ideas on how to adjust bios or whatever has to be done to recognise total size of drive. I am using win 98 OS. with 300+ ram. I hope this doesn't sound too confusing . thanks

[Omega]

You might need a BIOS flash to get your computer to *actually* recognize drives larger than X GB. I know there are workarounds, the most simple probably being to just partition the drive, but take a look for BIOS flashes first.