primary IDE controler(dual fifo) problem

hi i have a 4 gig packard bell and i have just added a 15gig hard drive on the slave but i have an ide problem if i unplug the 15 gig hard drive the ide drivers are alright its only when i plug in the second drive into the slave that i get the problem (this device is either not present not working properly or does not have all the drivers instaled code 10)i have even partitioned the 15gig into three 5gig partitions to see if that would sort it but its still the same and because of the ide problem my drives are working in MS DOS compatability mode file system and its realy slow.if anyone knows of anything i could try i would be greatful cheers