Blackscreen at loading a map (multiplayer)

Help! This thing started to bother me last time, because it didn’t do so many times before. Now many times (it looks like it’s more likely to go black screen than successfully load), when I try to join a server I simply can’t because I get a blackscreen and must try it again.

More info about the problem
The downloads or other loadings are finishing successfully, but the problem occurs at the last one- Sending client data. It usually takes long with 3… rectangles? (the marks indicating how far the loading is) remaining, but then, the last 2 are loading quickly and after that I can play. The blackscreen occurs at the 3 marks remaining, usually after the long wait, when I am expecting it to get to another mark.

Then I get a black screen and I can only see my cursor. Q menu or anything else does nothing, all I can do is to minimize it to see that I cannot work with the computer with that minimized and that the Gmod window is not responding, so I just shut it down through the task manager

My PC
Windows XP SP3 32bit
AMD Athlon 64 2.2GHz (single core)
Gigabyte Radeon HD4650 (1gb)
2gb o’ RAM