Dell Studio 1558 on the Intel i3, when the power supply is constantly blinking LED power socket. Checking feeds 3.3 volts is normal, and 5 volts unsuccessfully

What made you to find the cause of the problem?.

canot power on.
press power button 5v is down(variying)
(3v normal) and flasing led from dc socket
put new pwm (51427)& bios same as before
any help

What you have done is not enough to detect a fault. Looking for measurement. Make the measurement, perform the subsequent analysis of the situation on the basis of measurements carried out by you, and then ask questions. If you can not do that, then you nick here will not help.