green power led on
red HDD led flashing looks like harddrive working
if nothing on screen then
Video card US
mointor us (led on monitor lit?)
monitor cable US
I assume repair man plugged a good monitor to it to come up witj the diagnosis.
What machine is it? what op system?
graphics fitted--- card or onboard?
Open it up (with power off and uplugged, remove refit graphics card it may have come loose)click here