Hi officeofresearch,

 

Thanks for the post! As you mentioned the AC recovery option would be my first suspected cause for this, if that setting is correct I would suggest updating your systems BIOS and making sure the advanced sleep settings and wake on LAN options are also disabled.

If the problem persists a power button failure could cause an issue like this. If available I would suggest reseating / testing the system with a known good button from one of your other 990’s.  

 

For service manuals and the latest BIOS / Driver updates for your system please see the link below.

 

Product Support - OptiPlex 990

http://www.dell.com/support/home/us/en/19/product-support/product/optiplex-990/manuals

 

Thanks,

I'm not sure if the BIOS update would do anything, it's been working fine since we got it last year. I have other 990's that's running with the same bios version that is not exhibiting the same behavior.

I don't have an extra 990, so I don't want to monkey around with this system since a staff is using it.

Since we got the extended warranty, I think I'm just going to call this in and see if we can get a replacement.

Sounds like a bad motherboard. I've seen this behavior in many faulty optiplex boards.

Here's where I order parts for my company from: 990 motherboard

It looks like there's a cpu problem, dell online diag would crash the system at sse 4.2 test.

We're not buying 990 board since this is under warranty until 2017.

Is there a magic words that I have to say to the tech people when calling 800-456-3355, they don't seem to get the SSE 4.2 diag test reboots the system.

This is the 2nd system that exhibits random reboots. The first one took over 2 weeks to repair, two different techs showed up in our office, and they replaced everything bu the cpu.

Try replacing the CMOS battery.  I have had this issue with a number of Dell Laptops and HP desktops where you shut it down properly, but it turns itself on a very short time later.  Sometimes you also get a message about the time and date when you unplug and replug the machine, because the CMOS battery is no longer holding a charge (its what keeps the time and date when a PC or laptop is not plugged in or on battery power).  At first we also thought it was a motherboard, but I found it odd that I was getting messages about the time and date not being set. So I changed the CMOS battery, set the correct time and date in the bios, and the problems stopped. 

Conclusion: Try changing the CMOS battery (nickle sized battery) on the motherboard from another working PC to test the theory :D

-Alex V