|Tell us the make and model of your brand name system, or if you have a generic desktop system, the make and model of the mboard. |
The model, sometimes the make, of a mboard in a generic desktop system is usually printed on the mboard's surface in obvious larger characters, often between the slots.
The specific model of a brand name system is often shown on a label on the outside of the case somewhere, or it can often be determined by going to the brand name's web site and loading a program they have available, if Windows is still working, on the subject computer.
If this is a desktop computer....
Failing or dead power supplies are common.
If you can borrow a power supply from another working computer, try connecting that.