Hi TS... If you have basic knowledge in computer then you can identify the root cause of both failing PCs.....
Try this:
1st PC: (Does the windows logo appear? and it just fades after few seconds? follow this;
If you have Vcard, try not to use it. directly plug your VGA cable to your Motherboard.
If you don't have Vcard then you have a failing MOBO. Try to swap your MOBO from your second PC.
2nd PC:
Try to check your powerbutton. (basin naka press nana pirmi so mag on/off jud na)
Try to check the wire for the power button.( basin naa napaksit then naka touch sa casing/ground)
Try to clean your hardware.. remove/reinstall all hardwares..
If problem still persists, try to swap your Power Supply from your first PC.
naka nindot ani kay 2 imo PC nya pwede nimo e diagnose by swapping...
If problem still persists? hulat lang sa uban suggestions.. heheheh