I've got a PC with MSI K8N Neo4 Platinum motherboard inside
It turns on, but speaker doesn't beep, display stays in sleep mode, coolers works (except small one on the south bridge, it seems broken), hard drive buzzes.
But what is very strange for me is that this PC turns on immediately after electricity comes to it.
The pins which are responsible for the power button look ok, there is no dust, they are not connected to each other.
I have the same problem on a P4 487 socket Intel PC and nothing I've tried since mid August has worked so far.. I have replaced the RAM, cleared the BIOS, tested all the hardware on another system and the only component pending is the Motherboard which seems to have a slightly puffed processor capacitor. The capacitor is about an inch tall, and was puffed probably a milimiter but I have seen motherboards with several capacitor that were puffed a lot more and some had even leaked and were still running apparently normally, so I have to doubt this capacitor is actually the problem.
What I have found is that this problem is very comon, it can happen to a used or new motherboard, it can happen suddenly and w/out a previous glitch.
Some people have solved it after reinstalling or replacing the RAM modules or cleaning the sockets, replacing the Power Supply, resetting the BIOS. I restored another PC with the apparent same problem after cleaning and repacking the thermal grease on the processor, but I havent had luck and probably won't have it with the Intel 478
Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.
Make sure you plug the CPU power cable in. The system will not boot without it.
I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case once you are finished.
You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU. Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.
If no beeps: Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.
At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire (standby power supply): 5 volts always on. The green wire should also have 5 volts on it. It should go to 0 volts when you press the case power button, then back to 5 volts when you release the case power switch. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.
The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.
A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.
This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.
If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card.
Silence, long single beeps, or series of short beeps indicate a problem with the memory. If you get short beeps verify that the memory is in the appropriate motherboard slots.
Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST. At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.
Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
Thanks for advise in advance, hope today i will try them.
But one black spot i want to eliminate:
"You can turn on the PC by momentarily shorting the two pins that the case power switch goes to"
In my case, in turns on without shorting those 2 pins. I just plug it into electrical outlet and my PC turns on.
Can anybody explain me these ?