Asus K55VJ Won't Turn On

[sb1370]

My laptop was working fine until I opened it to clean it up (according to the same model video guide) and didn't take the main board out of its place.
I put every thing back and then tried to turn it on, the power indicator turns on but nothing happens: no display, no fan sound, no HDD indicator and sound,... . I have to unplug it to turn in off.
What's the problem?

 

[learningbitbybit]

Try this: remove the battery and the power supply and hold down the power button 30 seconds. Then plug in the AC adapter and try to boot up the laptop. The power supply might also be dead but that is very unlikely since your power indicator turns on.

 

[sb1370]

Try this: remove the battery and the power supply and hold down the power button 30 seconds. Then plug in the AC adapter and try to boot up the laptop. The power supply might also be dead but that is very unlikely since your power indicator turns on.

I tried hard reset, no result.
Also the problem isn't power supply because even with battery it doesn't work.

 

[sb1370]

I took the BIOS battery out and put it back after some seconds, plugged in PSU and then pressed the power button, It turns on!
I don't know why holding down the power button didn't do the hard reset.