First check the display cord. May be video section problem.

Frist of all listen is there any beep comes from from CPU, 
if beep comes then problem may be With RAM or Display card 
and if no there is no beep then check CMOS Battery,Physical 
connectivity and wires of SMPS.

ther r three main problems
1) if we put the resolution high then the no visualaisation
2)See the output device(Moniater) is connected properly
3) then check the VGA(Visual Graphics card)
  correct me if i am wrong

1) Check the power cables is properly inserted or not.

1. check the power switch ON and Pluk point is connected  
2. If its Ok . Then Check the power cable connected 
properly on Backside of the monitor Mostly it may be loose 
connection)
3. if its ok. Then check if any Beep sound is coming from 
CPU and the SMPS Fan is working 
4. If its ok . Then Replace the Monitor with Spare Monitor 
and Test

our computer is made by mainly two device.1st of all we 
check which one is defective.for dis we check hair 
attraction on monitor,beep sound,status of key board LED,cd 
tray in or out.than procced according to status.