ok.. straight up, please just save it into a notepad file next time.. its easier than me scrolling down a long post
To tell you right now, we're making progress, but not doing as much as i'd hoped lol..
There are 4 factors to a game to not run: 1. Software conflict 2. Inappropriate hardware and 3. Not enough power and 4. Temperatures, last two usualy ties into the 'hardware' catagory.
Hardware we can cross off you meet the requirements. For me, this system sounds like it was custom built for you, correct? Then there are a few more troubleshooting i'd like you to do. Print this instructions if you need to.
-Turn off and unplug your PC from the wall. Take the screws on the back holding the case access side off and slide the case off.
Check the PSU info:
-Usualy on the top rear corner of your PC there is a box where the power cord from the power socket goes into and on the other side has a bunch of wires going to different components of your pc. Look for a label that has your info on it and write them down, then post them up here. An example of this looks like this:
http://i61.photobucket.com/albums/h47/N3051M/PSU_Lable.jpg
Dust(and a bit of Temperature)
-Clean out all the dust buildup while you're there.. use a can of compressed air or a brushto dislodge any stubborn particles
-I'm guessing that you have 3 or 4 RAMs installed on your motherboard (512mb, 256mb, and/or a 128mb), from the info given from Everest. Sometimes mixing RAM sizes isn't a good idea, so for troubleshooting take them all out, and find the one that is your 512mb one, and leave that in slot 1. Boot up your PC and try to play HL and see if its a bit more stable now. If it does seem better then you just need to buy another stick of RAM that is the same size and type as the one you currently have (to make it 1GB).
Software we've crossed off drivers being the conflict.
-You can also try exiting/turning off all the other background programs and see if HL2 makes a difference, as well as reinstalling HL2, updating it through Steam etc..
However i'm still waiting on your Minidumps files. Instructions to find them are in my previous post.
If you don't have any, then its either that you've disabled it or it doesn't seem to 'need' to generate one (which is ok).
In the case that its been disabled, goto the
My Computer icon on the desktop and right click>Properties. Find the
Advanced Tab and under
Startup and Recovery click on the button
Settings.
Uncheck
Automaticaly Restart and under
Write Debugging Info select
Complete Memory Dump from the drop down menu.
In particular the info i was trying to get from you from Everest was this one, sorry if i wasn't to clear of it before:
Don't worry about making another report, just write down what you see on the readings at the moment and post it on here, and one more while you're playing HL2 for a few minutes.
Don't be afraid to tell me what other things you've tried to 'fix' this problem of yours, so i know what you've done and what doesn't work eg: reinstalled HL2, look for a patch, tried playing HL2 in window mode or a lower resolution etc.