Slave Drive not recog in my computer but it is disk...

I recentlt purchased a 80G hard drive which i tried to use as a slave in a Gateway desktop (the computer Os was upgraded to XP from Millenium a number of years ago w/o any issues) everytime i tried to format the 80G i received an error message 98% thru formatting stating that formatting was incomplete- after speaking with a Gateway Tech- he suggested i change the 80G to the Master and the factory installed HD (20G) as the slave. I changed the jumpers for the new configuration and installed the OS to the 80G- I can now see both drives in BIOS and in Disk Management but not in my computer. In Disk Management The 20G disk1 does not show a drive letter associated with it. When I right click on the blue bar I only get a delete partion option on the drop-down menu. I have data that i don'w want to lose on the 20- can you please advise as to how i can get the computer top recog the slave- Thanks in advance