half-life 2 crashes on “loading” screen

so i install the game, get the updates and all that crap.

turn on the game; the valve screen, the copyright info, and then the main loading screen where it says loading at the bottom. during the loading screen, it crashes. how do i fix this?

comp=
pent 4 2.53 ghz
512 ram
radeon 9500/9700 pro
sound blaster live! card

i have no trouble running doom 3 on high settings, so why should i now? this is really pissing me off.

PS demo a few months ago ran fine…