You sound ambivalent about my inexpensive PSU? It's not the cheapest/ it cost 1/2 of other PSU's. My old PSU was in the same price-category. It functions fine after 10-25 button presses and the hard drive boots. Before that only the fans spin/no video.
I'm not able to test components outside the case as you suggest. I have no on-board video.
In my response to worldlibrary I established that the on/off button functions. Something is "telling" the pc to turn off a second-or-two after it starts...until the 25th try-or-such. Is the "warm-up" effect of repowering the circuits likely to affect any specific component first?
You lean toward the motherboard as failing. If so: Why would it function perfectly as long as I leave it powered-up? The same argument would hold for the PSU and the video board -- right?
I'm now logging-off WinXPpro (vs. powering-down) and am able to logon the next day easily. (I used to power-down for 12-18 hrs. and then reboot the next day.)
I'd appreciate help from anyone reading this.