dell vostro 2520 some times working dv15 mlk mb 11280-1 pwb:mxrd2 rev:a00

So what`s the problem ?

the fault does not trigger some times trrigger

Knob?

knob????

trigger????

switch

So check the switch.
And let me give you a good advice. As the call so the echo.
If you want to get a good answer - be so kind tell us all about the problem.
Is it fair enough ?

no switch problm switch working properly but cannot power on

Give us complete information about the problem.
Did you sew the bios? Did you check or change the cmos battery?
Did you check all powers? Etc.

put dc jack system automatically power ON working properly.
all power is ok.
but the problem is system turn off and cannot ON.

3-4hrs after system working (automatically power ON)

OK, but why you so insistive that the switch is working good?
Don`t you think that the switch could have not good contact ?
Did you replace it with normal one?

without working amphere 0.020

Is it suspicious? Its normal cos the the board has a standby mode when the small part of the board is still working.
DID YOU REPLACE THE SWITCH WITH NEW ONE???