I suggest you step by step follow check it your Desktop issue.
A> All power plug proper connect or not, if possible change another port.
B> Have your ups get power or not, If ups on then nest step follow.
C> Check it SMPS on or off position. If your power ok and come to smps or smps not start then you SMPS damage position, you check it smps ok conduction or not..
SMPS more wire available you see it one more bulk wire available and black wire and green wire cross check, if not start smps then damge. But my friend if you smps ok or your are wrong wire attach then may be your smps damage. So better contact good Computer Hardware Technician.