So recently my 2009 Mac Pro has been turning off randomly. Now, I was able to get it to stay on for 20 minutes, then it turned off and now wont even start. The power light wont even turn on - it clicks but nothing happens. What could be the issue? It's been hot lately, and I do have 4 hard drives and an Nvidia 6870 gpu. Even with cpu temp in the 30's, it still shutdown and wont turn on. Is it the psu? What can I do?