graphic card not working

My graphic card ports did not work for a year or so. I opened the computer to finally fix it (because I wanted to have a 2nd monitor). I saw a PCI Express power cable missing and plugged it into the card. Then the graphic card fans started spinning (noisy) and the ports working. 5 min later...

Hello, I recently bought a new gigabyte geforce gt 1030 low profile graphics card to replace my AMD Radeon R7. The poblem is whenever I install it my computer won't turn on, but once I take it out my computer works perfectly again.