PC wont boot up

[avinash_545]

Hi everyone.

I have a small problem with my pc.
Actually, I just switched it on today and I found a spark coming out of the power supply.
I immediately turn everything off. I troubleshooted the problem to be the power supply itself. (I tried another working power supply on it and the cpu fan ran...so I concluded that everything was fine).
But now that I have bought a new 550W power supply, connected every wires.... the cpu just wont boot up, I have no image on the screen, the cpu lights (red and green) doesnt light up, but the cpu fan runs. Also I didnt smell any smoke, so I supposed all components are ok.

Please anyone help.

PC specifications:
power supply 550W
graphic card nvidia 6200 512M
512MB RAM
HDD 80GB

[avinash_545]

Correction: the lights are switched on when the power supply is first powered on then they turn off.

[gerbil]

Can only guess.... if system lights show then go off I have to think that something pulls down the power supply sense circuit and it then switches off internally some supplies to the mb. The drain could be from anything... graphics card, RAM, CPU, drives. Try disconnecting all those: pull the graphics card [does your mb have onboard graphics?], unplug power from hdd, leave only one RAM module, and try again.
If you don't have integrated graphics in your mb, then pull the vid card and connect oyur hdd... listen for disk activity/watch the hddd led at boot for activity [you won't see anything onscreen].
If still nothing then I could suppose that your mb silently died.

[avinash_545]

Another thing I've noticed is that as soon I turn on the power supply, the whole system is as if switched on with the CPU fan turning full throttle. This never happened before unless I myself switched on the system.

I will try what you told me hoping that the mb did not died.

Thanks.

[avinash_545]

Another thing I've noticed is that as soon I turn on the power supply, the whole system is as if switched on with the CPU fan turning full throttle. This never happened before unless I myself switched on the system.

I will try what you told me hoping that the mb did not died.

Thanks.

[gerbil]

I think I understand that... you mean that when you switch on the PSU by its own switch [usually on the rear panel] the system turns on also. The system power switch on modern mbs is basically a transistor latch operated primarily by a switch impulse from the front panel button; it also has software-controlled inputs from the mb [normal & emergency shutdowns, BIOS controlled shutdown]. So it seems as if that transistor latch is damaged to the point of being always on. Pretty much, the CPU fan should also start at a low speed until control inputs tell it to throttle up, or whatever. Sorry, but I'm thinking major mb damage here to several component systems. Fan speed control is usually integrated with fan speed and temperature sensing plus voltage sensing into one IC. eg a Winbond monitoring IC. I don't know your mb, but that chip may also have power control built into it.
A spark in the PSU could be the result of a brief short-circuit in there and who knows what voltages it sent thru what wires?, or a component burning out under overload from a sudden failure in a supplied circuit eg the mb.
Best of luck. I could point out that most mb problems are not worth fixing unless under warranty.

[avinash_545]

Yes the mb is really dead. I've tried everything you told me. The pc wont boot.

Thanks for the help though.