Power supply, Motherboard or Vista SP1 causing shutdown

[beegeebee]

Computer boots into Vista ok but, then shuts down within 3-4 minutes! Whilst this has only happened since the SP1 and later updates automatically downloaded, I don't really think that's the cause. It also occurs when I boot into XP pro which is on a separate HDD.
System is :- Antec 450watt Smart Power supply; motherboard Gigabyte GA-965-DQ6; E6300 core 2 duo; 4x 1gig sticks memory; Samsung 16x +/- DVD RW/RAM; Samsung 320Gig HDD; Western Digital 250gig HDD; Graphics Radeon X1650XT 256DDR3;
Vista is on the WD disk and XP is on the Samsung. Am currently using daughters comp to make this plea!
Any help appreciated as wife is tearing out her hair as I chat to her during TV!!! Aaaaah.

[ACtheTROLL]

sounds like it's overheating

2 possibles .... the processor looks like a fluffy bunny
or if you've moved the box .... or been delving about .... its possible youve cracked the heatsink thermal seal

somewhere in your motherboard stuff ( or on the website should be a temperature monitor

if not ... download and install
http://www.cpuid.com/pcwizard.php

see what the temperatures are like

[beegeebee]

ACtheTROLL. Many thanks for the rapid response. Will now go home, give it a try in safe mode and see if I can stay out the wifes way! B.

[beegeebee]

ActheTroll. Well I am now on bended knee to your superior knowledge! Am on line from my own computer. As you surmised the fan on the CPU had indeed come loose! Now fixed and the wife is now conversing with me in grunts of one syllable!! Brilliant. Many thanks. B.