Dell Optiplex 755 Won't Start

[RVB]

I've been given a 2007/8 Dell Optiplex 755 which has been in storage for a few years. Unknown why it was put into storage.

When the power button is pressed, the fans come on and it begins to power up for a few seconds then switches off again. Nothing appears on the monitor.

I've disconnected various bits (HDD, RAM, CD/DVD, internal speaker, button battery) hoping that one might be faulty but nothing makes any difference.
I checked the HDD and RAM in another computer and the HDD is dead but the RAM works fine.

I'm now wondering if its failure to power up even to a BIOS screen is a motherboard fault? However, it's very clean inside and there are no signs of puffed/leaky capacitors or other worn-out looking parts.

What do you think?

[peterperkins]

Replace the button battery unless it is already new .

Reseat the RAM and try again.

Presumably it will need a working disc drive with OS to boot.

[Mr Pointy]

Does this model have a PSU self test button on the back? Give it a press if it does.

[RVB]

peterperkins said:

Replace the button battery unless it is already new .

Reseat the RAM and try again.

Presumably it will need a working disc drive with OS to boot.

Thanks.
I already tried a HDD from an identical computer with same Windows version (still wouldn't startup) and have taken out the RAM to test in another computer and refitted when it checked out OK.

I will try a new battery later. It's quite likely the battery is low but would it cause a failure to start? Normally the computer will just say 'system battery voltage low, press F1 to continue' before it powers up (or something like that).

[RVB]

Mr Pointy said:

Does this model have a PSU self test button on the back? Give it a press if it does.

Thanks. I'll check that later along with the new battery that's also been suggested.

[Durzel]

From my memory of the Optiplex 755 the green light will come on, then go off, and then a few seconds later come on again. Presumably it doesn't do the second bit?

[Jinx]

My Dell studio 540s (similar vintage) - won't start at all if the CR2032 battery is dead. Replace and try again.

[buggalugs]

Check the mobo for swollen or leaking capacitors

[RVB]

Durzel said:

From my memory of the Optiplex 755 the green light will come on, then go off, and then a few seconds later come on again. Presumably it doesn't do the second bit?

Yes, green light comes on for about three seconds and then everything shuts down.

[RVB]

Jinx said:

My Dell studio 540s (similar vintage) - won't start at all if the CR2032 battery is dead. Replace and try again.

Tried two different batteries - one brand new, one used, but no improvement.

[RVB]

buggalugs said:

Check the mobo for swollen or leaking capacitors

Everything looks remarkably clean with no swollen or leaking capacitors that I can see.

[RVB]

Mr Pointy said:

Does this model have a PSU self test button on the back? Give it a press if it does.

Can't see a PSU self-test.

[RVB]

anonymous said:

[redacted]

Just tried that and made no difference.

[bigandclever]

Might help .. https://www.manualslib.com/manual/356816/Dell-Opti...

[RVB]

bigandclever said:

Might help .. https://www.manualslib.com/manual/356816/Dell-Opti...

Thanks.
Light 1 comes on very briefly but light 3&4 stay on until it powers off.
That decodes as memory failure.

I swapped RAM with an identical computer and the working computer was happy with the non-working one's RAM, while the non-working one still didn't work with known good RAM.

There are no beep codes unless no RAM is fitted.

[xeny]

You could try reseating the CPU, that's about the only set of electrical connections you've not touched at this point.

[Jinx]

xeny said:

You could try reseating the CPU, that's about the only set of electrical connections you've not touched at this point.

I'm was thinking the same - strip the machine down, replace the thermal paste, give it all a good clean (blow dust out with air, wipe with isopropyl alcohol - make-up brush and cotton buds - proper tear-down and clean). Put back together in the most minimalist way - one stick of ram, one hard-drive - see if you can just get the machine to post.

[bigandclever]

RVB said:

bigandclever said:

Might help .. https://www.manualslib.com/manual/356816/Dell-Opti...

Thanks.
Light 1 comes on very briefly but light 3&4 stay on until it powers off.
That decodes as memory failure.

I swapped RAM with an identical computer and the working computer was happy with the non-working one's RAM, while the non-working one still didn't work with known good RAM.

There are no beep codes unless no RAM is fitted.

Just to clarify, only one module?

Otherwise .. “NOTICE:If you remove your original memory modules from the computer during a memory upgrade, keep themseparate from any new modules that you may have, even if you purchased the new modules from Dell. If possible,do not pair an original memory module with a new memory module. Otherwise, your computer may not start properly”.

[Durzel]

Dells can be a bit funky and esoteric, but what I tend to do in situations like this is unplug everything except the CPU and PSU, and then try booting it. You'd get a load of beeps (assuming it has a speaker, it ought to) but then you'd be further along in diagnosing the thing that's stopping it from coming on at all.

[eeLee]

pull all pullable things from the motherboard - drives + power, CPU, RAM, video card. See if it does the same with nothing connected at all. Then put things in one by one starting with CPU and then RAM and video.

You will then start to understand whether the PSU is toasted or it's something else.