Computer power-up problem

[Chris Hogg]

Computer is Dell Optiplex 780

Normally, when I switch on at the wall socket, the computer briefly springs into life, lights blink and the fan spins up for a second or two. Then all goes quiet, and I push the 'start' button on the front and it powers up normally, and the 'mains on' light comes on again.

Now, as soon as I switch on at the wall socket, lights come on, the fan powers up and the computer starts beeping furiously. The fan continues to run, lights stay on, but the beeping stops but it doesn't shut down again waiting for me to push the start button, and the mains on light stays lit. Nothing else happens, i.e. The only way to stop the fan and turn it off is to press and hold down the 'start' button again to switch the whole thing off.

Any suggestions? Power pack failure? Bad caps?

[Andy Burns]

replace CMOS battery?

[pinnerite]

When you say the fan continues to run, I am guessing that you mean the case fan. If I am correct, when you next power off, disconnect the supply (to avoid mishaps) and remove the side panel.

When you next connect and power up, watch the processor fan. indeed if you can get into the BIOS or UEFI when you reboot, you might get into the menu option that allows yo to inspect various temperatures. This may point you in the right direction.

HTH

Regards, Alan

[Dave Plowman (News)]

My old desktop sort of does that, but says processor fan failure in the bios start up page. pressing F1 gets it going just fine. Been like that for years. The processor fan is running, BTW.

[alan_m]

The number of beeps and their frequency/sequence may tell you what is wrong

For instance

For instance code 1-1-2 on that page means a sequence of:

1 beep, 1 beep period without a beep, 1 beep, 1 beep period without a beep, 2 beeps.

Many motherboards have a coin cell battery in a holder. This battery may/will need replacing after 5 to 10 years. This is often the cause of a stalled or incorrect boot.

[Mr Pounder Esquire]

Why turn it off on the wall socket? You could be upsetting it :-) My 11+ year old computer has on the odd occasion been showing "no drives found". It has been doing this for over 11 years. Ctrl/alt/delete and it boots up fine. Worth a go?

[Chris Hogg]

Thanks for the suggestions. I took the (in my case) top off it and powered it up. There are two fans, one in the power supply and the other on the CPU. I assume that's standard. Both fired up, but then both died away as they should do for a normal start-up. In other words the fault was intermittent. Bugger: they're always the worst.

I'd never heard of beep codes. Next time it happens I'll take more notice and count them. I thought it was just throwing a hissy fit. Before putting the top back on, I wiggled a few plug and socket connections in the vague hope of achieving something. I don't think it's the cmos battery, as that was replaced only about 12 months ago. But it's something I'll look at if it throws another fit.

Thanks again.

[Mr Pounder Esquire]

I have been told that the battery lasts for many years if the computer is just turned off and not unplugged from the wall.

[alan_m]

At one time in the distant past the battery may have been rechargeable but later on they fitted lithium batteries designed to last perhaps 10 years with the computer on or off. Many people changed or scrapped computers before the battery failed. In addition, at one time a battery maintained the BIOS information but for the past few decades this is no longer necessary with flash/EEPROM memory.

[Andy Burns]

I don't think they last that long if the machine is left unplugged and the CMOS is being powered by the CR2032 battery, rather than via the

+5VSB rail.

Turn any nodern machine off, pull the CMOS battery and see how much of the BIOS config is saved in flash ... none of it.

[alan_m]

Incorrect and has been for many years.

The battery is now usually there to maintain the Real Time Clock when the power is off.

[Andy Burns]

If the BIOS settings were stored in flash, that would be dangerous, because removing the battery would not allow you to recover from incorrect settings ...

[The Natural Philosopher]

there is generally some shortable pins to 'reset' to defaults

[Andy Burns]

That just shorts out the supply to the CMOS, so is essentially the same as taking the battery out, how would shorting some pins remove dodgy settings from flash?

[The Natural Philosopher]

yoiu have a processors with inputs that controls the flash, It reads that pin and resets...

[Chris Green]

But it would need to have some power to be able to do that.

[T i m]

If / as / when it does, it might be worth un / re seating the RAM.

Leave it all plugged in but turned off at the wall. Touch then keep some skin in contact with the metal of the chassis / PSU and push the levers at both ends of each RAM socket simultaneously to eject the module and then carefully but firmly (making sure you *don't* try to flop the module over sideways) push each one back in (thumb at each end), observing / checking that the levers at the end are full closed.

This generally cleans / wipes any tarnishing that may have appeared on either the DIMM or socket and it should be good for another few years. ;-)

Cheers, T i m

[Steve Walker]

Could still be the battery. I replaced my watch battery and within a couple of weeks it was flashing the LCD display. As it is an analogue watch with an additional LCD, I ignored it for 12 months, as I didn't want to pay for a repair to what I thought was a fault (last repair cost £350.

After a year, the battery died. I replaced it and everything went back to normal. Must have been a faulty battery.

SteveW

[Andy Burns]

I suppose it could store some sort of checksum of the BIOS settings from flash into CMOS, that would get zeroed (or at least scrambled) by removing the battery or shorting the pins, then some sort of auxiliary microprocessor could zero the flash if the checksum fails before the main CPU boots ...

[alan_m]

But you don't lose the settings when the battery goes flat and you take it out to replace it!