About computer problem

[SAIKAT123456]

Hello,
I 'm in problem with my computer .I have an old configuration computer AMD-ASUS. When I'm working with it suddenly my monitor goes blank, M.board LED and HD LED become flickering but LED on the M. board is still lightning .Power goes off and then comes again, same problem happen few days ago but automatically after sometimes became OK. I could not detect the problem whether it is main board problem or cable problem or HDD problem.Plz help