You need to think and try all scenarios why your pc video card is not working properly.
I have the list but it depends on the situation of your pc.
First: Check the pci card if it is separated from the motherboard. Then check the slot if it is properly installed. Removed and insert again make sure you return the video gard 90 degree for proper installation.
Second: Check if you can go directly to the bios of your pc if blue screen then your video card is working. If you see any display on your monitor then your video card is working. If the display are bleared and sudden hang then the pci is the problem.
Third: Push the button on and off the for 3 seconds to check the display. If no display check your power supply if it is properly installed.
Four: If the problem is the motherboard built-in video card then you will need a hot blower gun to remove the chips and replace into new one. Write the chips set product code and search in google the compatible chips for the replacement. You can buy online for the chip set.
Fifth: Reheat the video card chips using the heat blower gun temperature 385F (195C). Check your motherboard handbook the ideal temperature for the reheat.
Six: Use only a small amount of thermal paste and spread evenly over the surface using a piece of cardboard.
Seven: Try using a good condition monitor for the display.
Materials you need to prepare:
Heat blower gun
Small amount of thermal paste
Video card replacement