What boot disk are you using?
What new parts did you install?
Can you remove some RAM and boot?
Can you remove the graphics card are you the built-in graphics?
As a diagnostic, can you go back to the older power supply?
The most likely issue is how you installed the new graphics card. Please provide some details. Some graphics cards require a three stage process of getting it right.
I started with a windows 10 boot disc when that failed went to linux mint that failed as well. It got to the initial linux download screen but then froze and shut down.
I installed an evga 600 w power block. A radeon rx480 video card. A 1tb western hard drive. As well as a stick of 8gig ram to go with the other stock sticks. .
I will replace the stick with the original and see how it goes
I can remove the graphics card as well ill do one at a time.
And if I go back to the older power supply I cannot run my upgraded video cars. But i know the computer didn't have this issue before.
I can't install the graphics card until I get access to the operating system. Should I try to start without the card in first?.
Sorry if I sound so ignorant