|Oh, SMPS is the power supply. I had to google that one.|
In order for a computer to work the power supply must provide several different voltages at sufficient current. LEDs usually need 5 volts; fans need 12 volts; drives need 5 or 12 volts or both. In addition to those voltages, a motherboard also needs a 3.3 voltage source and a -12 volt source. Here's the pinout of a typical power supply showing the voltages it supplies:
Sometimes a power supply will fail to provide one or some of those voltages so that some peripherals may work but the computer as a whole won't work.
Based on your brief description the power supply seems to be the likely problem, although that is by no means a certainty.