I'm having problems with my PC, I need to explain everything really so please donate me a few minutes and your opinion! 
To start, here's the specs:
(I know the following is a marathon read, but I'm pretty stumped and the simplest of suggestions could help)
When building the PC, I put the Hard Drive in the computer etc, and put my windows CD in and booted up. When it got to the stage of Windows setup which did the formatting bit, I tried "Full Format" and got sometime along the lines of "Format failed, the hard disk may be damaged". Then I tried "Quick Format" and got the same message. So I tried it on another SATA socket and the same happened. So I tried with an XP SP2 disk, same happened. SO I tried on a XP SP2 Corporate Professional disk, and the same thing happened.
Well getting a bit frustrated I put the drive in my brothers computer which already has Windows installed, booted up his machine, and formatted it using "Quick Format" (RClick my computer, manage, disk management, right click the unformatted disk, clicked Quick Format) and it did the format with no problems. But it was suspiciously quick, it literally just worked - a split second to quick format the 160GB drive!
So stuck it back into my computer, and installed windows onto the now formatted hard drive. No formatting errors this time as I had already formatted it in my bro's computer.
I installed drivers from the ATI website (6.14's), and then Call of Duty 2, which ran fine on full graphics.
Then I installed Company of Heroes, which also ran fine.
A couple days later I went to run Company of Heroes, and I got an Infinite Loop error... since then it hasn't run.
I tried updating to ATI CCC 7.1, but no difference. I tried all the things suggested in ATI's website, too, and have googles endlessly for a fix for th Infinite Loop error.
I tried DirectX updates, too. And windows updates.
I installed Half-Life 2 and Counter-Strike Source. CS:S didn't work, it said "hl2.exe - application error, memory couldn't be read"... But half life 2 works fine on full graphics. Whatever, it's a problem with the game (I thought), but all of SteamPowered.com's suggestions didn't help - nor forum posts that google gave me.
So ok, stuff this, back to Call of Duty 2 - which worked fine for a couple of days, but now since yesterday refuses to load the game. Menu is fine, but it just exits to desktop after clicking join game.
I installed Doom 3 today, it runs fine on high settings even today. So does Half Life 2 (well, haven't tried it today actually, but was fine yesterday) but not CS:S.
I ran memtest86, which passed my memory 5 times now, and the memory's running at 2.0v, 800Mhz, 5-5-5-15 timings.
I've just run Western Digital's diagnostic tools, which passed my hard drive on Quick Test and Extended Test (which scans for bad sectors).
I've run orthos which shows everything as perfectly stable. Intel TAT shows reasonable temps..
EDIT: and S&M passes everything, although first time is crashed on Cache Level 2, but worked after a restart. Also SuperPi doesn't give any errors.
I dunno what to do. I'm going to TRY a reformat... but to be honest, if I manage to reformat without my brothers computer now he's at uni, it probably still won't make much difference. I'll keep you updated on that.
Can anyone help me? What's up? Any suggestions on what you would do under the circumstances?
Running processes are the normal bare minimum with AVG anti-virus and Realtek HD Audio Manager.

To start, here's the specs:
(I know the following is a marathon read, but I'm pretty stumped and the simplest of suggestions could help)
ThermalTake Silent PurePower 560w PSU
160GB Western Digital Hard Drive
Sapphire X1950 XT 256mb
Gigabyte DS4
E6300 Core 2 Duo @ stock speeds
1024mb Kingston HyperX CL5 RAM
When building the PC, I put the Hard Drive in the computer etc, and put my windows CD in and booted up. When it got to the stage of Windows setup which did the formatting bit, I tried "Full Format" and got sometime along the lines of "Format failed, the hard disk may be damaged". Then I tried "Quick Format" and got the same message. So I tried it on another SATA socket and the same happened. So I tried with an XP SP2 disk, same happened. SO I tried on a XP SP2 Corporate Professional disk, and the same thing happened.
Well getting a bit frustrated I put the drive in my brothers computer which already has Windows installed, booted up his machine, and formatted it using "Quick Format" (RClick my computer, manage, disk management, right click the unformatted disk, clicked Quick Format) and it did the format with no problems. But it was suspiciously quick, it literally just worked - a split second to quick format the 160GB drive!
So stuck it back into my computer, and installed windows onto the now formatted hard drive. No formatting errors this time as I had already formatted it in my bro's computer.
I installed drivers from the ATI website (6.14's), and then Call of Duty 2, which ran fine on full graphics.
Then I installed Company of Heroes, which also ran fine.
A couple days later I went to run Company of Heroes, and I got an Infinite Loop error... since then it hasn't run.
I tried updating to ATI CCC 7.1, but no difference. I tried all the things suggested in ATI's website, too, and have googles endlessly for a fix for th Infinite Loop error.
I tried DirectX updates, too. And windows updates.
I installed Half-Life 2 and Counter-Strike Source. CS:S didn't work, it said "hl2.exe - application error, memory couldn't be read"... But half life 2 works fine on full graphics. Whatever, it's a problem with the game (I thought), but all of SteamPowered.com's suggestions didn't help - nor forum posts that google gave me.
So ok, stuff this, back to Call of Duty 2 - which worked fine for a couple of days, but now since yesterday refuses to load the game. Menu is fine, but it just exits to desktop after clicking join game.
I installed Doom 3 today, it runs fine on high settings even today. So does Half Life 2 (well, haven't tried it today actually, but was fine yesterday) but not CS:S.
I ran memtest86, which passed my memory 5 times now, and the memory's running at 2.0v, 800Mhz, 5-5-5-15 timings.
I've just run Western Digital's diagnostic tools, which passed my hard drive on Quick Test and Extended Test (which scans for bad sectors).
I've run orthos which shows everything as perfectly stable. Intel TAT shows reasonable temps..
EDIT: and S&M passes everything, although first time is crashed on Cache Level 2, but worked after a restart. Also SuperPi doesn't give any errors.
I dunno what to do. I'm going to TRY a reformat... but to be honest, if I manage to reformat without my brothers computer now he's at uni, it probably still won't make much difference. I'll keep you updated on that.
Can anyone help me? What's up? Any suggestions on what you would do under the circumstances?
Running processes are the normal bare minimum with AVG anti-virus and Realtek HD Audio Manager.
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