Crash at least 3 ways

Question

The build:

1. Ivy Bridge 3770K 4.5Ghz HTon, EISToff, C1C2C3on, TBoff.
2. Team Group 8Gb 2400Mhz Dual Channel DDR3, in slots 1 and 2 of MotherBoard.
3. Gigabyte UD5H (BIOS F14).
4. AMD 7950 x2 in XFire (slots x16 & x8).
5. Antec 750W Bronze 80+ PSU.
6. Windows 7 64Bit Premium Home Edition
7. Avast FREE Anti Virus.

The Problem(s):

1. After initial boot, from 5 or more hours of inactivity the system powers down within 1s, proceeded by rebooting. Not a BSOD, KSOD, Freeze and no message or comprehensible log of the PC acknowledging the failure other than a Critical Event 41 on power up.
2. When watching a networked Stream video the PC freezes and has to be powered down by one of the external buttons.
3. Freezes during graphics intensive game. Peripherals which all have LEDs go dark and unresponsive, sound and image stuck in loop.
4. This I think is unrelated but I still want to fix it; Error Events 102, 7001, 7023 happen every boot, and every half hour or so. They are PNRP and other Peer Networking Services. I have 1000s of these logged.

Notes:

1. Temperatures (Motherboard, CPU, PSU and Case) are all less than 75% Of threshold.
2. RAM is working, tested with Memtest86+.
3. Intel diagnostic, determined CPU is fine.
4. Drivers and BIOS is up to date.
5. Registry is crisp clean.
6. Windows is up to date.
7. Neither Virus nor Malware has been detected upon search.
8. Problem 1 always happens, Problem 2 happens once every two days at least and Problem 3 can happen recurrently or not at all.

Answer 1

This is likely to either be a problem with your graphics card or sound card. Those are the routes I would go down first. It does sound like a driver issue as well, so you might want to try some older drivers to see if it helps with stability.

Another thing to try is run prime 95 to check your cpu for errors. Sometimes diagnostics tools are not always accurate as the CPU doesn't always trip up unless under heat and load.