Crashing on map change

This happens no matter what I’m doing.

Fretta, HL2 Campaign, or just simple sandbox maps- the game will crash me whenever I attempt to change maps, or when the server I’m on does.

.

ive had problems like that where all the source games would randomly stop working, what i did was wen to program files/steam/steamapps and deleted source engine.gcf than ran a game and it fixed it, besides that i wouldent know what to do

Intel® Pentium® 4 CPU 2.40GHz
1.02 GB of RAM
RADEON 9250(possably the most unsupported card made by ATI. I’m changing this, soon.)
and Windows XP

As for changes, I’m just running a clean installation for now since I mostly play Roleplay and Fretta servers and rarely ever host for my friends.

Apparently, the problem involves materialsystem.dll

But the rest is just a bunch of addresses and things that the computer thinks I understand

So, nobody’s going to help beyond quoting a part of the rules thread? thanks a lot