Apple IIe disk drives don't power up at startup.

I have a well loaded Apple IIe. The drives worked at one time, but now they will not power up. I have swapped the controller card with another , and tried it in a different slot. I have also swapped the 1 and 2 drives. Nothing happens when I start the computer - I do get the Apple II at the top od the screen. I have a SCSI are and hard drive connected. It does work. How can I get the disk drives to work?