Stack Rebooting problem

[AmitBokade8335]

I have 6no. of Cisco 2960 switches. 3 switches are joined in Stack 1 and other 3 Switches are joined in Stack 2 with a UTP loop cable connected between Master switches of Stack 1 and Stack 2. The above configuration was working for the past 1 year then suddenly one fine day all the 6 switches rebooted automatically at the same instant. When show version command was run , all showed "System returned to ROM by Power On " . Now this event has already happened 5 times and i have checked the UPS AC power fed to the switches, changed the power source of stack 2 switches to a different UPS , then also same event occurred. Now i am strongly beginning to suspect that there may be some issue other than Power but Now i am lost for ideas and desperately in need of some help.

[AmitBokade8335]

IOS version running of all the switches is 15.0

[Leo Laohoo]

If both stacks rebooted at the same time, I'd still say it's power.
Post the complete output to the command "sh log on up det".

[AmitBokade8335]

Please find the files for Show log on up detail command to all the 6 switches.

[Leo Laohoo]

Can you post the complete output to the command "dir flash2:crashinfo_ext"?
Get the output from both stacks.

[AmitBokade8335]

SOrry for the late reply,

But when i run the dir command on both stacks no crasinfo file is not found.

[Leo Laohoo]

It is a power issue.

[AmitBokade8335]

Since this issue has occurred 5 times already, Suspecting switch version problem ,we have upgraded the IOS software version from 15.0 to 15.2 in the upper stack , keeping the lower stack at 15.0 only and also added a seperate switch with no connection and same configuration as the stack to eliminate whether the problem is actually related to power or it a connection realted issue or a IOS version issue. Now Waiting for the problem to happen again so that we can move forward.