System not booting....pls. help...?

its my cousins PC. he faced same problem earlier and changed SMPS (Rs.600)a year ago. It is a 2 yr. old assembled set. no beep sounds. however he removed the case, took out the RAM and fixed it tightly again. he says that he doesn't note any other abnormalities inside. what could be the possible problem ? CPU light(when button is pressed)does not glow. what could be the possible problem and remedy ?