SMPS stands for Switched mode Power Supply. It gives power to all the components in your computer system.
If your computer is dead and even not a single lights glow on your Motherboard, the basic need is to check is SMPS. To do so, remove power cable from SMPS and unplug all connections of peripherals (Hard disk, Motherboard, DVD etc). Now you can check SMPS easily
by connecting a small wire between green color(PS_ON) and black color
wire (COM) as shown in figure. After connecting, plugin power cable and
switch on the SMPS. If SMPS fan runs, SMPS is working.
Their are many other problem too, if computer is dead, but please try this step first.