dell r810 is not recognizing drives 4 and 5

I have a R810 that i have added (6) 146 gig SAS drives to. In Ctrl-R only drive bays 0 - 3 will show the HDD but, drive bay 4 and 5 is not recognized. I switch the drives around and still only drives 0 - 3 will show. I check the cables and connection but no success. any help trouble shooting this greatly appreciated.