If your computer does not power on at all, the most likely culprits are either Power Supply (desktop only) or motherboard.
No Boot or Blue Screen.
If your computer has power (you see lights, hear fans spinning), but nothing on the screen, or if the computer starts to boot up and then crashes with a ‘blue screen’, there are several possible issues.
NOTE: Any hardware changes must be done while computer is completely powered down and unplugged / battery removed!!
Try Safe Mode – if your computer will boot into Safe Mode, it is a software related issue.
Test Screen – If you hear the computer running, but see nothing on the screen, try swapping monitors or plugging in an external monitor for laptops.
Test RAM – try carefully removing the ram and powering on. Most computers, when functioning properly, will give a long, repeating ‘memory error’ beep. Power off and replace the ram, one stick at a time, powering on when ram is properly seated.
Test Video Card – if your computer has a removable video card, try removing it and either replacing it or plugging your monitor into the built-in video port if available.
If none of these things work, you are likely looking at a failed hard drive, corrupted operating system or failed motherboard. It is best to seek professional services at this time.
Article source :