To assist you better in troubleshooting, it would help to know how many times the amber light is blinking.  There are Diagnostic Indicator codes we can look up.

From memory the button flashes 2 quick flashes followed by a long flash, indicating motherboard as a broad diagnosis, but the Optiplex runs faultlessly for months at a time till the power fails for longer than my UPS can keep it running. The power up workaround I mentioned in my first post always seems to work now and then it runs as it should, sleeps wakes, reboots etc. From memory it never crashes or spontaneously re-boots either

Ok @the baz, do you want responses in this thread or the other one? - https://www.dell.com/community/Optiplex-Desktops/Optiplex-9010-Does-not-turn-on-Blinking-orange-light/td-p/6128509/page/3 

I am happy to keep it in this thread, but I only recently saw your reply in the other thread, so that is why I replied to it in that thread.

Hello @the baz

I've been having this same issue with a different behavior on my Optiplex 9010.

1. I would press power button but would not POST, amber light would start blinking pattern 2-1 (bad mb).

2. I have a workaround to power on as normal. I basically hold the PSU test button and sometimes fans go crazy and I have to disconnect power cable and try again.

Sometimes I press power button and turns right on.

3. When powered on. And I turn off the computer. It would normally turn on if the power button is pressed before a certain time (say 30min-1hour after shutoff). This would happen even if left on sleep mode. But after this certain time, it would show the same amber light and no POST again.

AND REPEAT...

I must add that I have changed the CMOS battery and ran hard reset (draining power and do CMOS reset) about 5-7 months ago and my computer worked flawlessly until recently this past month it has had the same behavior. (Last amber code was different as well, 2-3 if I can recall? But no certain)

I came to the thread because it seems we aren't the only ones experiencing this type of issue. I will try CMOS replace and hard reset today.

Could you please keep me (us) updated on the new PSU replacement?

I am suspecting that this may be a factor of failure in my PC due to all the electronics plugged in on same outlet.

I will do some testing also, will keep an update on this post.

Thank you!

Will definitely post an update when I fit the PSU or if I discover anything new

Baz

I have the same blink sequence (2 short 1 long) meaning bad M/B.  My work around is unplugging the psu, removing the newly replaced cmos battery, holding down the power button for 1 full minute and then powering back on.  I don't understand why the M/B could be bad if it runs all day after doing this.  Any help would be appreciated

Meanwhile, I'm going to suggest the BIST Test on YouTube.  I see now they call it "retired," but I like it better than their newer one.  The distracting background music drives me nuts in the newer one.  The BIST test is a good way of checking various computer components.

You might also try going into the F12 Boot Menu.  Select Diagnostics.  Run full diagnostics.  It might take hours, so one can always let it run overnight.  There is the quick option, but if nothing comes up, you'll wind up running full diagnostics any way.

Dell Support Assist can also scan you PC and do diagnostics.  Full will probably take at least 40 min.

I did the BIST test a while ago and from memory it passed when everything was connected. The power supply would start for a short burst of fans and lights on but would not boot up. I will maybe revisit the test when I get the new PSU after I shut it down. I will also try the Dell diagnostic over night and see what it comes up with.