New Home Built PC unexpected shut downs

I have just completed building a super powerful PC comprising of:

Intel QX9770 quad core Processor 3.2ghz
Intel DX48BT2 Motherboard
8gb RAM (4x 2gb DDR3)
Sapphire Radeon HD3870 graphics card
2x WD 300gb SATA HDD's as RAID0
LG Blu-ray/HD/DVD/CD drive
Windows Vista Ultimate 64bit [full retail]

All the latest downloads and up-dates are installed.

I can be working away, the PC could have been on for a few minutes or an hour or more and it just shuts down and re-starts for no apparent reason. If I look in the Problems, Reports & Solutions section it simply states that windows shut down and is awaiting a solution - it doens't say why!

I know the usual culprits include over heating - can't be, apart from three huge great fans, it sometimes occurs just minutes after starting. RAM being another problem, I've tried taking out all but one stick of RAM, and replacing that with another - it is unlikely all 4 sticks are shot, they are matched sticks.

Is there any reliable software out there that can monitor the system and give more accurate reports as to what might be the problem? I have also reinstalled Vista after formatting the drive.