PC doesn't turn on

this morning i overhaul my computer..blow the dust etc..then after that i attach them together..and whoala..my computer doesn't turns on..

it will turn on..like 30min.of waiting..then when its turn on..it will hang..then i will restart the pc..using the reset button..but nothings happen..i mean it will reset..but it will not boot..then i will shut off the AVR..then i will turn on the AVR again..then Nothings Happen..means only the monitor is switching on..but the system is dead..

i try to short the power switch of the motherboard..but nothings happen...i try to short the green and black..and grey and green in the power supply unit..its fine..i try to clean again the RAM,the Vcard,but its the same...

please sir..help me..i really2 need your answer here..:(:(:(
 
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