Steams having problems

[Nex]

i have this problem with all of my Steam games, mai9nly only Day of defeat source and counterstrike source.
both get the same problem, they start up fine and all good and i enter a server and it seems to be ok it starts loading, up until at one stage it freezes and u can move the mouse but u cant cancel you cant log into windows, u cant do anything besides withe manually restarting your computer, or you wait for ages and finally a Blue Screen Error comes up, i think it has something to do with memory?
anyway, does anyone know how to help me with this problem, or fix it?

also i have manged to get an error screen and it comes up saying this:

CmeshDX8::LockIndexBuffer

and that seems to be an engine problem.

[SilverTears]

This may be a similar problem I have been having on another computer for years, and it's still not fixed.

When it freezes, does the sound loop over and over until finally you get a blue screen and have to restart manually?

[Nex]

it has sometimes but usually it doesn't play any sounds and just freezes, then after about 2 minutes or longer, boom blue screen.