Hello everyone. I recently made my own pc because my old one's motherboard was broken. I took some of my old parts that worked in my old pc and put them into the new one. I'll give you a list of what I bought new and what I transfered.

New Parts:
PSU - 750W
Motherboard - ASUS x58 Sabertooth
Case - Cooler Master HAF X Full tower case
New Heat Sink (Universal)

Old Parts:
9GB DDR3 Ram
ATI Radeon HD 4870
CPU i7 920 @ 2.67ghz

After putting the parts together, the computer worked fine for about 3 days. I even left it on overnight so that I could install windows. After I was done setting up the computer, I go on it and downloading a game called Team Fortress 2. After playing 5 minutes on it, the computer shuts off, the GPU fan goes loud and only a black screen shows. I then unplug turn off the computer, reboot it and the GPU fan goes full speed again with a black screen. I tried seating the graphic card on another PCI slot but the same thing happens. When I unplug the power from the GPU and turn on the computer, on screen it says that the power isn't connected to the GPU. After connecting it, the fan goes loud and only a black screen appears. Does anyone know what the problem could be?

Are you saying the screen is now always black when the video card is correctly connected w/ the power cables from the PSU?

Should I make a video to show what I mean?

You could just answer my question.... and clarify the current status of the system is. It sounds like you don't have video at all?

I know I worded it wrong. What I mean is that on boot, my GPU fan goes full speed and there is nothing showing on screen.

And this is the way it stays indefinitely until you shut it down? Does anything show up on the screen during POST? (This is before the HDD is accessed, just BIOS, CPU and motherboard components info flashes on the screen)

1. If yes to both questions, then... It sounds like the video card is broken. simple way to check is pull the video card, replace with one you know works, and try booting.

2. If yes only to first question, and the POST screen displays, and the screen goes blank only as/after Windows is loading, then it's most likely a driver issue.

Because he said, "When I unplug the power from the GPU and turn on the computer, on screen it says that the power isn't connected to the GPU." apparently the computer will post. Still I would swap out video cards or try integrated video if possible.

Yeah. Thing is, there are no other cards i could use and there is no intergrated video.

maybe the old mobo was not really broken and it was the video card thats really was bad....?
also check the ram with memtest86+ if you have another PC to check it in.