DELL Vostro failed POST: no DELL Logo but monotonous beep sequence

Question

DELL Vostro 3560 had always been running perfectly. But now after some time of having not been used on startup the POST failed:
After Power-On the three service LEDs flicker like being used to. Hereafter in most cases nothing more happens except of a repetetive beep sequence, a short beep being followed by a pause of ca. 3 seconds and this continues on until switching off. The DELL Logo does not appear except in some rare cases (about 1 in 10). Then no beeping and I can start BIOS Setup. In such a case I fullfilled all possible system tests and all results with no error, even the extended memory test. The system Disk (SSD) does not cause the error. The failure is independant of having the battery and the HD mounted.
Does anyone know about this monotonous beep sequence not being mentioned in the handbook?

JOcean · Answer

The beep codes are listed here. One beep indicates a motherboard, BIOS corruption or ROM error. It could be a simple matter of a weak CMOS battery especially since the problem is erratic. The instructions are listed here but it is a bit of an involved service procedure.

Rudobra · Answer

thank you for helping me to understand the beeps and giving me hope by your hint on the battery. Unfortunately now after disassembling and re-mounting the hardware with a new LI-Cell all my hope is gone. I again run the DELL test procedures from BIOS and also the Support Assist from within windows when the system once in a lot of start failures succeeded to start. No error detection. And as I wrote when the system runs then it runs well - until shutting down. It is as if some irrelevat mainboard feature is detected to fail - but not always. Do you know if it is possible to restrict the POST in some way?
However thank you for taking care on my issue.

Rudobra · Answer

addendum: is it possible that just the fan is detetcted to run not as expected?Yet I do not know if I have to change just the motherboard or the complete unit with CPU, Graphic and fan?

AdrianG001 · Answer

The beep codes are listed here. One beep indicates a motherboard, BIOS corruption or ROM error. It could be a simple matter of a weak CMOS battery especially since the problem is erratic.

Rudobra · Answer

yes, thank you Adrian, that's what JOcean told me too. And so I've already tried to change the LI cell although the CMOS battery failure should signal the 'beep 5 times' - as I now learned. And indeed, unfortunately changing the battery had no success. In a German thread I found the sad information that for the VOSTRO there is no way to find more details about the mainboard failure:
DELL Vostro 3560 Fehlerton bei Start
But do you think that I just need a new mainboard or that even the CPU/GPU/fan mounted on the mainboard unit can cause that problem - what would mean that it's a total loss?