Error keeps occuring

[Madsenevoldsen]

I've been troubling with an error regarding my graphic card. A few weeks ago I re-installed the whole windows system, it has been running perfectly until yesterday. I decided to install Counter Strike Source, got it installed and updated on steam. Then when I was about to run the game, I got a message telling me that my graphic cards software was outdated, and got a link where I could update the software.
I'm using a 'ATI Radeon 9550 / X1050 Series' graphic card. I thought that it might be a good idea to download and install the new software for my graphic card, but I obviously thought wrong. Before re-installing windows, without the new software for my graphic card, this game ran perfecly, without any errors. But now that I've installed the new software I keep getting an error named 'Engine Error' that says "failed to lock index buffer in CMeshDX8::LockIndexBuffer" with the only option clicking 'OK'. Now when clicking 'OK' another error occurs now named 'hl2.exe - Program error' which says "The instruction at "0x10953e2c" referenced memory at "0x0e4ea1a0". The memory could not "read". again with the only option clicking 'OK'.
Now my question to you is, does anyone have an idea what may be causing this?

[smack323]

did you try to google the error msg? usally that will give ya a bunch of people with the same problem and most cases tell you a fix

[Madsenevoldsen]

Yea I've tried that, but that was no help to me. Figured it our though, the new software used to much of my computer to launch specific games. So an older software was the key for me : D