I own the following GPU: EVGA GeForce GTX 750Ti SC 2GB GDDR5 P/N: 02G-P4-3753-KR.  This draws power from the motherboard. Recommends 400W PSU

 
I decided to replace my 550W PSU because of a noisy fan with: EVGA 500 W PSU, P/N: 100-W1-0500-KR
 
After installing the PSU as instructed (minus the PCI/E cable, as my GPU does not need or have an input for this), I booted up.  Computer power seems to work fine, but my display is stuck looking for a source.  I removed the GPU to try and use the integrated display card, and had the same issue of black screen while monitor looks for a source.  I reinstalled the GPU and old PSU, and the display returned to functionality.
 
I've begun a return process with Amazon for the PSU assuming it's defective.  Would appreciate any comments if there's something else going on.

 
Welcome to the Forum ersenakici ,
Did you remove all the Cables from the older Power Supply and use only the Cables that came with the EVGA 500 W PSU, P/N: 100-W1-0500-KR Power Supply?
What do you mean "I reinstalled the GPU and old PSU, and the display returned to functionality" Did you remove The Graphics Card?
Did you test the PSU outside of the Case using the Paper Clip Test?
What was your Older Power Supply?
What Motherboard Make and Model do you have?
Or is this a Dell or an HP Computer?

Requirements

• Minimum of a 300 Watt power supply.
• Total Power Draw : 60 Watts