Grab a monitoring utility that will probe your processor and MB ambient temps, along with a HD probe. Motherboard Monitor, although defunct, works well with most motherboards out there. If you're looking for a more recent and up-to-date program that does this, Speedfan works pretty good. But since your problems happen when you immediately start the game or whenever intense disk activity is happening, it'd be reasonable to say your system isn't hanging due to an overheating component. If you had a component that heated up that fast, and that quick, you wouldnt' be able to run any sort of game that put any load on either the CPU or the GPU because it would lock up in ALL of your games. Not just HL2. Another reason here, DX:IW and HL2 utilize DirectX, not OpenGL, since Doom 3 and Quake 4 work perfectly fine (and use OpenGL), that would make me think something's goofed up in your video drivers, or DirectX itself. Updating, or rather, re-updating DirectX may fix anything that's missing, and a fresh driver install might fix any other problems. I'd reccomend Driver Cleaner to really clean up the crap that's left behind from driver installs, which gives you a fairly clean environment to put your new version of display driver on. Monitor your system first, see if anything. One note about updating your BIOS, if you have to do that, which would seem unnecessary to me, you may need to have the latest chipset drivers for your motherboard handy when you flash the BIOS.
I've had a problem with both HL2 and VTM:B, both use the same engine, Source. I had mouse-lag issues that were extremely bad, I mean, twist and wait two seconds then the camera would respond... that's how bad it was. I would get constant lockups in HL2 and VTMB would plain refuse to run. At first, I thought it was the new MX-1000 I bought at the time, turns out it wasn't. It was something way deep in the system and the only solution that worked for me was very unorthodox. Now, I'm not saying that this is the only way, and I kinda sound a little repetitive here, but the only thing that fixed my problem was a clean wipe of the hard drive, and a fresh install of XPSP2 and all the drivers at thier latest revisions. Source tended to be extremely picky about mouse drivers, for me, in the early versions of the games. It could be fixed now, with patches and such, but I'm not sure as I haven't loaded up HL2 on this new build of mine.