Non BSOD crash gaming related

Having intermittent crashes were my computer powers itself off and restarts itself, just like hitting the reset button. There are no error messages, No BSOD, no recovered from critical error and no memory problem.
It has done it rarely when I am on desktop or using the internet, maybe 3 times in 12 months.
Worst is when I am playing games that are so so for graphic needs, min specs on the one game is at least a 64MB video card. WHen I am playing it can crash and do the reboot once to several times a day or for however long I am playing.
My system is a year or so old, never had many problems untill that last 6 months maybe.
And lately playing Portal2 results in at least one crash every 3-5 minutes of game play.
Specs are:
RocketFISH 700W PSU
Phenom II X4 940 Black edition (not overclocked)
8GB DDR2 1800 RAm, (think its 1800, its the highest you can go for DDR2)
Asus M4A785-m (I think, not positive) Recent Bios updated
ATI Radeon HD 4850 512MB
WD 1GB internal and WD 1GB external (OS on internal)
Stock heat sink and fan that comes with the Phenom Core
Lots of space in my case and have 2 120MM fans and a smaller 80mm fan going.
Core Temp.exe tracks my average temp at 49C when idle and average 56C when gaming, isnt a big deal, its always ran like that with no problems
Never had a heat issue with it,

Is there a way for me to find out if there is an error that is causing my computer to crash like it is, once I have a handle on that error code (if there is one) then i can fix it up. If not I would most likely start buying parts and peices until i either A, have a new system or B, replace a faulty something or other.
Never had an issue with anything crashing. 700W should handle everything. Video card is like two years old but hasnt given me so much as a burp. Same goes with the processor.

So here is the attachments in .rar format, dont have winzip for .zip but should function either way

Not sure how far back the data was pulled from but have not had a problem with Defender crashing since i tossed essentials. IDM that I use on occassion is very useful for me as far as management and download times are a lot faster than without, but it is set to not go from certain websites and types of downloads. It doesnt auto. But like you stated neither of these would cause the crashes described if changed. Its been running this way, IDM and BD on my system now for two years without issue. I recently did a lot of force closes via task manager on the essentials and other system resources in order to try and solve a memory issue, If i leave my computer on for more than 3 days or use it extensively in browser it seems to build up a lot of used RAM that i cant seem to purge with programs. Methinks that firefox and chrome has major leakage, but even with them close out it can sometimes read up to 70% ram in use, which is high for the 8GB that I have, BD does take up more than what I think it should. And after scrubbing and testing my ram extensively there isnt anything wrong with it, So i can rule bad RAM out. and my system is really rather clean, despite some dust bunnies that cling on and i cant remove without dissassembling my PSU.

oh and ive run the gambit of virus, malware, spyware, etc on it and clean as a whistle

Yes, its my intent to still use BD, hence the load at startup