If there's no power at all, (no fans, no LEDs etc) that most probably is a bad power supply. In a rare case, that can be the motherboard too, but usually you will see fans spinning even with a bad MB. So check the PSU.
To manually check the power supply, you will have to turn it on first. You have to ground the pin#16 or in simpler terms, connect the green pin with a black one and your PSU should start. Then you can test each pin with a Voltmeter. (***BUT REMEMBER TO HAVE ALL THE OTHER EQUIPMENT CONNECTED OTHER THAN THE MB. since usually they have a minimum load requirement. And conclude the test as soon as possible***)
Orange = 3.3V
Red = 5V
Yellow = 12V
And btw, I guess you have only offbranded PSUs back in SL, Most people get the cheapest PSU or the one that come with the 4000Rs case. But trust me, that can be the biggest mistake, I see computers fail all the time with those cheap-o PSUs