Computer switching when Windows loads

Hello,

I have an annoying problem with my PC randomly switching off when Windows is loading. It will finally load Windows on the second or third attempt. It will also switch off when Windows has loaded and I'm logged in but this is rare. The PC usually boots okay in safe mode. It seems to need time to 'warm-up'.
I have replaced the case and PSU but no luck. Fans are working okay. Speed fan shows the following info with some hot temp readings and a couple of suspect voltages:

VCore1: 1.26V
VCore2: 2.48V
+3.3V: 1.82V
+5V: 5.67V
+12V: 4.86V ?
-12V: -10.96V
-5V: 0.48V ?
+5V: 5.08V
Vbat: 3.01V

Temp1: 55C
Temp2: 45C
Temp3: 25C
HD0: 42C
HD1: 29C
Temp1: 47C
Core: 50C

Fan1: 2109 RPM

Motherboard: ECS 6100sm-m2 with dual AMD 64 core.

I'm at a loss to know what's going on.
Has anyone had the same problem and solved it?

Thanks,
David.