I had this problem at first, where my game would crash as soon as I loaded a new game, and my computer would automatically reboot. Here are my current specs:
AMD 1400 768 DDR RAM Geforce Ti4200
I run Halflife 2 at 800x600 with advanced settings to medium, HL2 runs perfectly smooth.
What you need to do is simple; before you initially ran Halflife 2 you were asked to upgrade your video card drivers. All you need to do is roll back this driver. Go to "My computer", and right click> properties. Now click "Device manager". Then, go to your video card tab, and double click it. At the driver tab, click "Roll back driver". Once done, restart your computer, and Halflife 2 will be running without any crashes.
Took some time to figure it out, but this seemed to fix it completely.
I didn't make it!
can gforce ti400 (is it this?) be compared with ati radeon 9250?