|If the computer isn't sending a display to the monitor, it could be any number of issues. Does the monitor display anything on screen when you first boot the computer, or are you connecting it while an operating system is running? Is the system emitting any beep codes? If the graphics card is removable, does it work when it is connected to another computer? Is there more than one graphics card in the computer?|
And so on, and so on.
Also, we don't know enough about your current power supply to know if it can easily be swapped. Some systems have proprietary power supplies that are difficult to replace.