dell poweredge 2900 server wont detect sas drives.

i have a second hand dell 2900 server. it seems it wont detect the raid card or sas drives. i installed a 500 GB hard drive through sata port on the mother board and it detects it. i installed windows server 2012 r2 on and updated both bios and Windows to its latest one. it still wont detect the sas drives. i tried down loading drivers through dell website ether i cant find it or just says wrong one driver what should i do.