This is the weirdest thing, I'm not a PC Noob, yet I'm on here asking for some help. First of all I will say that both My GTX 750 SC and OptiPlex 380 and a intelC2DuoE8500 where bought from ebay(For a budget build for a friend). I first booted Up the Computer with The new E8500 and It started up fine, I set up windows and everything. Then when I turned the pc off I put in the GPU, no post beep, the fans where spinning at a steady pace(Unlike usual). No Graphics where comming from the GPU(Vga cable is connected to a DVI adapter), so then I plugged in my vga cable into the Motherboard, no onboard graphics either. So then I thought Maybe it's the cpu, So I changed It out, and The onboard worked when the Gpu wasn't inside the system. Then I plugged The gpu in, then it didn't work. So I went back to the new CPU. I then Plugged in an older Gpu and It went Through POST, I was getting Signal through the Gpu. That made me think that it is the psu, So I changed the psu to an Old inspiron Psu that I used to have a i5 3330, and a GTX 750 ti sc running off of. I plugged everything in. And the same problem occured. Then I took the Gpu out to see if it was faulty, I put it into my Pc and It worked perfectly fine. So then I thought maybe I'll reset the CMOS. I did that, and it didn't work, same problem. I have no Idea what I can do at this point, as The Pci-e Slot isn't faulty and 300watts Should be enough to run a GTx 750 Sc and a IntelC2Duo. PLease Halp me. 
