all VMs suddenly reset

[MehdiJavadi]

i'm newbie in virtualization and have a HP G8 Server that runs ESXi 5.1U3 on it,

nowaday something weird happened

ESXi not rebooted but all VMs suddenly reset

how can i check esxi logs and security issues?

and i am going to upgrade my ESXi to 6.0U2,

could you recommend me?

THNX in Advance

[Techie01]

ssh into esx box and look at files inside /var/log directory. That is the log location