I have a 2010 2.8ghz quad core Mac Pro and now when I switch it on the computer turns off after like 3 secs itself. Sometimes it stays on but I get a black screen with no chime nor anything else.. nothing happens. I already changed a new power supply and even bought a Radeon 580 sapphire pulse for it. Still the same... I can’t find out what the problem is.. What else can it be..? When boot up the display card fan switches on running then after a while it stops. Is that normal? I don’t even see the infrared light under mouse going on so I assume it’s not booting or something. I do feel the hard drive is running tho.