HP Pavilion 8565-power/switch problem?

This PC’s harddrive died. I installed a new 80gig and plugged the cables in (the old drive remains because I can’t get to the screws on the back side – but it is not plugged in). After reassembling the case the power switch won’t work. No lights, nothing at all comes on. I had to remove the power supply to get the new drive into the cage but I rechecked all the wires and none were unplugged.