Daughters E-machine refused to boot

Last week my daughters E-machine refused to boot, and I couldn't use the recovery partion or CD.
Thinking it might be the PSU, I took one out of another computer I have but isn't working because of the Ram, unfortunately this didn't make any difference to the e-machine.

I tried some linux live CD's. which it ran for about 20minutes, so thinking I could let my daughter use Ubuntu for the night, I moved it back into her room, where it refused to work again.

Before I had changed the PSU, I had also reseated the fan and heatsink with new thermal paste, but likewise with the PSU, it didn't make any difference.

The funny thing was that I was able to run The Ultimate Boot CD and Hirens Boot CD with no problem, but was unable to run a O/S.

The next day I had to order a new Motherboard as that was the only thing left that could be causing the problem, so I ordered a Gigabyte M61PME-S2 from ebuyers, which I got the next day.

I took it slowly installing the motherboard, as it was the 1st new one I had installed so didn't want to mess it up.
Fitting the motherboard wasn't a problem, though I still have two wires not in right place and so have no activity or power on lights, which I don't see as too much of a problem.
The computer started fine, it was the re-install of windows Vista that took the time.

So I installed Vista which took an age, then the mobo drivers, unfortunately then Vista wouldn't restart, and I finally had to give up and re-install vista again and after it did a disk check,and cleaned off some of the old Vista program, things started to work until Unfortunately I suffered a few BSOD's, so in safe mode I removed the last program I had loaded, and from then on it seemed to work.

I wasnt' sure about the re-activation of vista as I had changed the motherboard, and it wouldn't work with the key on it, but when I used the product key from the back of the computer, it activated no problem.
Finally my daughter had a working computer again.