My Computer Can not Display on the monitor or send power to Usb

Hello Everybody,
Just got a new HP 600BM desktop computer about two months old. last week, it breezed for some time that i had to force shut down. After that the system could not display anything on the monitor. when you start the system, the HDD spins, the fans spin, Power-ON LED lights but it doesnt boot and it doesnt show light on either keyboard or mouse. if you press on DVD eject button it ejects but the screen remains blank. The Mobo does not show any sign of burn or damage.

I have tried all manner of solution like

Reseting Cmos,
Pressing and holding down power button for 30s and 1min while every peripheria is off the mobo,
Removing cmos battery for some time.
Removing and reseatting the RAM
none of them worked.


Note: The system has no internal PSU. it has just the kind of a laptop charger.
Has no expansion slot, so must use the onboard VGA, USB and the rest.

can any body be of a help, its urgent