HP Pavillion 23" AIO won't power up, Motherboared PWR LED flashes briefly!

I'm hoping someone else has had this problem or has seen/heard of it before. I have an HP Pavilion 23-H TouchSmart All-In-One computer that won't power up. Initially I believe it took a power surge and cooked the mother board and power supply. I have replaced, Motherboard, CPU, and Ram Power supply. Whereas before when I first looked at this unit there was nothing happening, no lights, fans, boot up, NOTHING. VOM confirmed power supply was dead. I installed all of the above new replacement components and the ONLY sign of life is the onboard motherboard PWR LED briefly flashes. I'm assuming as in other motherboards this light needs to STAY lit. IT DOES NOT. This type of AIO computer was very problematic and was discontinued after 2yrs. One of the many problems was a faulty power on switch mounted on the upper left outside frame. But again VOM says micro switch is functioning correctly on this unit, but without motherboard power (as indicated by PWR LED inside yellow circle in attached pics) how can it boot up?

Connect With Techlore