PowerEdge 2900 III keeps restarting itself

At home I have a Dell PowerEdge 2900 III running VMware ESXi 5.5U2.  I have had this server for over 3 years and it has been rock solid.  The last few days it seems to be restarting itself for no reason, and when I log into the vSphere client I don't see any alerts except for ECC corrected some errors on one of the sticks of memory, but that alert has been there for months with no issues.  At first I thought maybe it was a power issue because my battery backup recently notified me that the battery needs to be replaced, but I have another server and a switch plugged into the same power source and they are unaffected; I also have the second power supply plugged into a different power source.

Not quite sure how to pull logs from ESXi, or why the server would just randomly reboot.
MikeIT ManagerAsked:
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Unless you have setup persistant datastore for them logs, or an ESXi Syslog server, the logs may not be available for viewing.

But they are in \var\logs (you will need to login via ssh)

They may not tell you much, how about the event logs on the server.

Check and Test the hardware, and Memory. (use memtest86+).

Check heatsinks, fans, cpus...

Update firmware and BIOS if applicable.

Are you using the OEM Dell version.... although if been stable for years, hardware fault.
MikeIT ManagerAuthor Commented:
I never set up anything for logs.  I've only been running 5.5U2 for a month but never had any problems previously.  I did use the Dell customized CD image for the installation, though.  I checked all the hardware and everything appears fine.  I will run Memtest on it this weekend and report back.
MikeIT ManagerAuthor Commented:
Just ran Memtest86 and it passed.  I'm contemplating going back to ESXi 5.1 U2 and seeing if I have the same issue.
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Any changes to your VM recently??? A misconfigured VM and cause host issues
MikeIT ManagerAuthor Commented:
The only new VM I made Recently was a SQL 2014 VM, but I have even kept off every VM except for VCENTER and a Windows 7 VM which was literally the first VM I loaded on the server with no progress; I even had it with just the Win7 VM on and it happened.  The last few days it hasn't restarted, but I don't know if that's a fluke or not.
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
How much memory in this host server?

are you using more memory, we've seen issues, where using more memory in the host, e.g. more VMs, memory is used in additional banks (DIMM slots), and the server restarts.

and THIS was not displayed on a memory test, and these were Dell 2950.

We fixed this by replacing ALL the memory in the Dell 2950 with new memory.
MikeIT ManagerAuthor Commented:
I am running 24GB (12x2GB).  I have made no changes to the RAM setup since I initially acquired the server.  I am VERY careful with watching host memory utilization and am usually at around 16-18gb in use if I have my usual VMs powered on and working at normal load.
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
I would isolate the memory DIMM with the ECC errors and remove.
MikeIT ManagerAuthor Commented:
It did it again last night.  I'm going to just wipe the server completely and install Windows on it so I can get some consistent logging from Windows and GFI EventsManager and see if it still gets flakey.  Thankfully I have no VMs of any real need on there since I moved my personal e-mail to Office 365.

I'm starting to think that putting more money into this box would be a lost cause, and am contemplating just buying something newer with more storage and faster CPUs/RAM.
You could always save money and move your lab to the cloud
MikeIT ManagerAuthor Commented:
Sorry, have been busy haven't had much time to play around with this.  Tonight I went ahead and wiped the system clean and installed Windows Server 2012 Datacenter so I can have some sort of usable logs.  Setting up a couple VMs in Hyper-V and we'll see how it goes.

Compdigit44 - I prefer having the hardware on site, it's more cost effective.  I did move my email from Exchange 2013 on-premises to Office 365 which was the best decision I've made in a while.
MikeIT ManagerAuthor Commented:
Still crashing.  Only thing Event Viewer shows is an unexpected shutdown.  About to give up on this and just buy some new used servers.
MikeIT ManagerAuthor Commented:
Seems I didn't have the second power supply plugged into a different power source like I thought.  Problem was my bad UPS.  Removed that from the scenario and everything is running like a clock

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MikeIT ManagerAuthor Commented:
Was an environment issue not related to the server itself.
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