Since I had to reformat my hdisc and reinstall windows, I copied my HL2 saved games, reinstlled windows, reinstalled HL2, and copied the saved games back to the HL2 folder.

Now whenever I load any of them I get a message on the bottom right corner of the screen that says "AI disabled". I can move around freely and everything but the enemies just stand and do nothing.

It only happens if I load one of my saved games. If I start a new game everything is fine.

Is there anything I can do to solve this? I don't want to start the game from the beginning...

Well, what do you know... patching solved the problem.