hl2 prop error

The problem started when I used a 3rd party defrag for my steam games my computer turned off and when i started up garrys mod i couldn’t use most of the useful and comic props. I first un installed hl2 and reinstalled it but that didn’t work and i also did the same with garrrys mod but that didn’t work either. this problem is also apparent in source forts and some of my other hl2 mods. But this problem isn’t in tf2 or my other steam games.

I run a…
Windows Xp media center editon sp 2 with an intel R pentum D with 3.00Ghz with 1.5 gigs of ram