This is definitely not an issue with the Intel® Graphics Controller so perhaps our Server Folks can help us with this so let me move your post to the Server Community.
I was checking our hardware validation list and I was unable to find this newer video card listed. Have you tested the 750 card in another system to make sure it is functional?
I would also suggest updating the BIOS to the most recent release BIOS 98. You might as well want to disable some of the unused onboard solutions such as serial ports, onboard RAID, audio for testing purposes to free up resources in the BIOS.
Make sure you uninstall the drivers for the Radeon 6450 HD befor removing it from the system. Then remove it and install the new graphics adapter.
i get no display at startup, even at bios start so graphic drivers in windows got nothing to do with it, so far im waiting for new powet supply - old one got 670 watts but its poor quality, possibly 12v line is not secure and efficient for 2x CPU 8x2gb fbb dimms and rest of MB (drives, vents, etc. ), old graphic card has power consumption about 30 watts so it works fine, new one is powered only by pcie slot, and need about 55-60watts, pcie supplies up to 75w but with my old PSU its not giving enough power, so gtx 750 cant initialize correctly possibly thats why im not getting signal on dsub, it makes sense specialy when you consider that modern high efficient Gpu's are very vulnerable for power supply problems. so thats my idea so far - i should get brand new nice quality PSU about friday so then we wills see if its correct