My 2010 Mac Pro gives me only a blinking power button when I try to start.

My 2010 Mac Pro gives me only a blinking power button when I try to turn it on. The external drives turn on but not the computer or monitor. I've tried holding down the power button to restart but I still get only a blinking power button and no start. It's running IOS 10.8.5 and I use it mainly for recording and mixing music. I use Digital Performer and sometimes ProTools. Nothing new has been installed lately.

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