mack1

A couple of items have not been mentioned concerning the power supply. Some cases have a switch that is made when the cover is installed to enable the start button. Look for this.
Also, if you have a volt meter, check the power cable that connects to the mother board. I don't recall the pin number, but one pin supplies voltage to the board even when the computer is powered down. That voltage is required for the start switch to work. When you press the start button, it shorts the two pins together where the start button wires connect to the mother board and brings in a relay inside the power supply. Once this is done, power is supplied to the mother board and fans come on and the post starts. The 450 watt ps should at least make an effort to start the system, and will probably work for all equipment plugged in.