there are a few steps to fix the problem:
1. Turn on the PC, look if there's any beeps or messages on the monitor screen. if nothing of these happens then keep troubleshooting.
2. Unplug the PC power cord from the main power circuit. hold the power button for 5 seconds. then open the pc case and blow all the dust out of your pc with compressed air. Do not use your mouth to blow air on them because it contains moisture that can lead to short-circuit.
3. pull the ram sticks out of the dimm slots. clean the DIMM slots with compressed air make sure the slot is completely clean, even a piece of hair can cause the problem. clean the ram sticks. and re-install them by pushing in the DIMM slots
and make sure that they are locked perfectly...