So I recently got my hands on a Mac Pro 3,1. It was missing RAM so I bought some 667MHz from Ebay. Here's my problem; it boots, but when I select my El Cap usb install disk the mouse pointer freezes and nothing happens. I've tried three different flash drives and reset SMC and PRAM. Also, when I press the power button there's a single clicking sound from the case. Same when I press it to power off.