Optiplex 745 Blinking Orange Power Light

Hello everyone this is my first post here. I own a dell optiplex 745 with a core2duo 1.8 Ghz processor, 2 gb RAM and have also added an XFX HD 5550 to it. I have been using it since almost two years, and it hasn't caused me many problems except this blinking orange power light.

The problem is just this that the desktop just won't start. All that happens is that the power light just blinks orange. This has happened to it almost four times in the last two years, and the problem has seemingly resolved itself the last four times. Well it would go something like this: I would turn off the PC normally, and the next time i started it all i would get is this blinking light. Then after a couple of days or hours, I would try again and it work as if nothing had happened. But this time it happened four days ago. I turned it off, then switched it on but i got the orange light. Since then, I have tried so many times but this time I fear something much bigger has happened.

Now I have done a decent amount of work in trying to figure out whats the problem. The key thing to note is that its not my PSU (yes i used a different one). Does this mean it's my motherboard which is causing the problem? Or is it something else?

I did a bit of digging up on the internet for the same problem, and I saw one which said something about a faulty power on button       http://www.instructables.com/id/Fix-the-Dell-OLOD-Orange-Light-Of-Death/ 

I havent tried it but I would like some views on this from people here....

Also I found another one which says the problem is caused by faulty capacitors on the motherboard, and they said to just change them, but when I checked the motherboard, there weren't any with bulges on top or any liquid coming out of them etc   http://www.ccl-la.com/blog/index.php/dell-optiplex-745-repair/