PC turns on...but no display. Monitor and cable
I fully agree with you.
Capacitors have gone bad in the power supply. This causes a weak power rail.
Enough power to spin fans, and light- lights, but not enough power to turn on the Processor. (Harddrive is inactive because there is no processor running)
Power supply's are rated in Watts. (Volts x Amperes = Watts)
1.ALL the lights use less than 1 Watt.
2.EACH fan uses 2 to 3 Watts.
A typical Processor uses 55 to 125 Watts!
Depends on the processor.
BIOS won't turn the processor on, and hand the computer over to the Operating System, (Example: Windows XP), because there isn't enough power.
I DO NOT advise opening a personal computer power supply!
Those Electrolytic Capacitors I have referred to, hold a charge for WEEKS, sometimes MONTHS, after the power is disconnected to the power supply.
Capacitors are made to slowly build up a charge, then release it all at once!
If someone touches across the terminals of a capacitor, and it's still good, it can release it's charge to them!
If someone touches a circuit that capacitor/s are in, the charge can be released to them!
Shock can range from BAD to FATAL!
It is for this reason that the best, and most effective method, is to replace the power supply with a known, good one for a test.
I realize power supply's do not grow on trees, and not everyone is a computer geek like me, and has several laying around, (I mean Tech, lol!)
IF you are stating this question referring to an eMachines that uses a Bestec ATX style, 300 Watt power supply, the cost is very inexpensive for a new one.
Not to slam a company, but Bestec PSU's are cheaply built, and this is the reason it failed. (IF yours is a Bestec)
You don't have to break the bank however, to replace this power supply with one that is much better.
An ATX style of power supply is a very common one. Approximately 85 to 90 percent of personal computers use this style of power supply.
This example would get you buy for quite sometime, (IF you keep the inside of the computer clean regularly, and the power supply, with a can of compressed air for computers. 75 percent of failed computers that come to my shop are dirty inside)
Just an example. Not advertising for the power supply manufacturer, not the website.
Have any additional questions I'm right here.