my pc do not turn on, why?

i was checking my drives with latest macfee antivirus. my pc turned off and now it is not working
the fan of SMPS is also not working but one light on mother board is on
even cd drive is also not open
i think SMPS is crashed coz my power connection has not earthing at my home
but untill now it was fine about 2-3 years
is it power-voltage problem or other virus problem
when i have checked my OS(XP) drive (C: )it not showing any virus detected
any idea?
what should i do if my SMPS crashed ?
can i repaired it? or i have to change?