Computer shuts down when cold?

I have a somewhat strange issue with a machine I built myself.

The machine was out together in May 2012 and ran with no issues until January. For the past two month the PC will shut itself off, and sometimes won't turn back on for an hour or two. Normally my first thought would be overheating, except that it only happens when it's cold in here. A fan heater in the room is enough to keep the machine stable. I'm relatively new to building machines and have never heard of this being a problem before.

Spec:

8GB (2X4GB) DDR3 PC3-10600 C9 1333MHZ
AMD BULLDOZER FX-4 QUAD CORE 4170 BLACK EDITION 4.20GHZ (SOCKET AM3+) PROCESSOR
GIGABYTE GA-970A-DS3 AMD 970 (SOCKET AM3+) MOTHERBOARD
MSI AMD RADEON HD 6670 2048MB GDDR3
700W PSU

 

I have built a lot of PCs and have never heard of this phenomenon, if a PC gets below freezing point (left overnight in the trunk of an auto) it should always be allowed to warm to room temp before it is fired up, cold can effect the hard drive during operation but this usually happens when a PC/laptop is operated out of doors in the cold.

I am not able to explain why a PC that has warmed up after starting should shut down in a cool/cold room because it is warm from operating.

I know you have said overheating is not the problem but that is the only cause of a shutdown i can think of.

Hopefully another member has experience of this and can help.

 

sounds like a dry joint or bad connection on the psu thats making contact when the pc is warm enough to expand whatever to make a connection

try re inserting the power leads from the psu to the motherboard

apart from that it's gotta be a dry joint either on the motherboard or within the psu
it's the only thing i can think of