MoBo does not go into POST

[Joop]

My Asus A8N-VM CSM socket 939 MoBo with Athlon 64 X2 CPU used to work without problem, but has now developed, without apparent reason, a strange behaviour.

More often than not it did not go into POST. Upon pushing the start button, the CPU fan starts, the HD light flashes etc, but the normal short BIOS start-beep does not come and the screen remains blank.

After several times switching off and again on, it did sometimes beep (the normal short start beep) and entered and completed the boot cycle.
When start fails, it never reaches the stage of indicating an error by means of error-beeps.

Bios version was the last available version, which is a beta version. This beta is already a couple of years old, but Asus has never made it final.

I managed to flash it back to the last, obviously older, non-beta version, but that did not help.

I tried whether removing three of the four memory sticks (leaving one) did change anything. No change.

Clearing CMOS, remove battery, check battery voltage, reinsert battery etc. No change.

I tried BIOS setup defaults. No improvement.
Strange thing was then that I could not make it to exit the setup cycle anymore. It did not respond to the keyboard.
I had to power off and (try to) restart.

I have flashed the bios to the newest (beta) version again.
Now a pattern seems to have developed: Most of the times (not always) it starts every second attempt.

Some Googling indicated that I am not the only one with this problem (and not only with this MoBo). However I have not found a solution in any of the forums. Quite often there is no response at all.

[edwin]

http://www.badcaps.net

bad capacitors. this one known contender...

[Joop]

The problem is solved.
The PC has two IDE channels:
Channel 1: two HD’s in master-slave configuration,
Channel 2: a DVD writer in master-slave configuration with a DVD reader.

I remembered that, when assembling the PC it was rather critical which of the DVD devices was master and which was slave. Of the two possibilities only one worked (yes, I know how to set the jumpers).

I decided to give it a try to disconnect both DVD devices. And, bingo, bios start problem solved!
Strange thing was, though, that when I reconnected both devices, there was no problem anymore either.

Yet, when the problem existed (i.e. sometimes the bios cycle started, and sometimes it didn’t), when it did start, the bios detected both devices correctly, and once Windows had started, the devices worked OK. So they were connected and configured correctly.

It would seem that leaving the configuration as it was could result in problems again, since the DVD devices did seem to be somewhat incompatible.

So I have now configured both IDE channels to consist of an HD and a DVD device.
For the time being the bios starting problem seems to be solved.

[edwin]

keep an eye on the capacitors on this board. and if troubles again replace the cmos CR2032 3V coin cell lithium battery. They officially last about 3 years. Can be 1, can be 10 but they do die slowly, can cause similar symptoms, just like the bad capacitor effect I mentioned before. good to see you solved it this way.

[Joop]

Unfortunately my statement thet the problem had been solved was too optimistic.
The problem is back again.

Every first attempt to start fails. No start-beep and the screen remains black. If I then keep the startbutton pushed until stop, and then quickly push it again, it usually starts. If I then don't open the bios setup screen (don't push 'del'), Windows starts normally, and runs without any further problem.
If I open the bios setup screens I can make adjustments as normal but leaving the setup proceduere with 'Save and exit' is not possible and results in a frozen bios screen. The keyboard freezes too.
Yet adjustments appear to be saved when checked at next start.

Another observation: At the end of the Post screen I always get the message 'Secondary slave- ATAPI incompatible'.
That happens also if I completely disconnect the secondary IDE connector (i.e. no secondary devices connected)
I have tried three different bios versions, Message remains the same.
With the secondary ID devices connected the devices are detected correctly, but the incompatibility message remains the same.

I have tried another power supply unit: No change.

Capacitors all look healthy wit flat caps and no leakage vissible at he bottoms.
CMOS battery is OK.

[edwin]

CMOS battery can only be known OK if replaced by a brand new one. Out of circuit it may still show 2.xx volts, in circuit it can be dead.