So I have a Dell Optiplex 780 MT and I recently picked up an EVGA GTX 750 TI to install into it, but when I turned it on, the PC kept trying to post but it kept failing. For the first two tries it gave me error code 1 3 4, but after that it gave me error 2 4 and it can't boot up. I researched and found that the issue could be because of my PSU, so I picked up a 550w PSU and installed it, but it did the same thing as before. I then tried upgrading the BIOS. I tried revisions A04, A12, and A15, but this didn't help. Can someone give me some help? (My current specs: Intel Core 2 Duo E8400, 10GB DDR3, 500GB HDD, AMD Radeon HD 5450.)