We have 4 PE R710 in a rack with other devices.  3 of the R710 are part of a VMware 3.5 cluster.  The 4th is a stand-alone VMware 4.0 ESXi (free version) machine.  On 7/22 around 4:07 all 4 reboot.  Nothing else in the rack did so there is no outside power issue.  All of the equipment plug into powerstrip inside the rack and then to the UPS.  The SAN showed no power issues.  The UPS showed no power issues.  3 other non R710 machines without DRAC did not reboot.  I'm wondering if anyone has any thoughts on where to start looking.  I've already spoken to VMwae support and review all the logs.  From the VMware view, the systems were turned off and on.  I'm wondering if there could be some CPU, iDRAC or something else on this hardware that reboots a machine and leaves no logging?