If you just pressed the power button and entered bios, the cpu will of course be a lot cooler. If you restart the machine after having it on for a while, bios might report similar readings to the gigabyte monitor sw.
Sandra might be looking at different sensors than the monitor software.
Those temps don't look high though - so I don't believe temp killed your system, perhaps it was a faulty PSU.
My bios reports similar readings as asus mb monitor and mbm5.
As those readings are often faulty, trust no one.
-M