Slave drive problem

Hello everybody im new to this website and i have a question regarding a hard drive. Up until recently both of the hard drives that i have worked fine. It is only after i cleaned the computer with compressed air that ive enountered a problem. When i hook up both master and slave drives the message pops up on the screen which says that operating system cannot be detected. When i hook up only the master drive it boots up fine. I am wondering if the slave hard drive is broken or do i need to run some set up. Your help would be appreciated.

Thank you