Sorry Stefano that I didn't look close enough at your log file, now I see things clearer.
Vendor: NVIDIA Corporation
Render: GeForce FX 5200/AGP/SSE/3DNOW!
Version: 1.5.3
You're running a pretty old graphics card. As a result, you get very tight limits for ingame textures:
Maximum texture size : 4096
Now that the Splashscreens themselves do have a size of exactly 4096kb and there are several other textures to be loaded at game start, everything looks like your GPU just can't load the Splash Screen into memory due to texture size limitations (remember that your GeForce FX 5200 GPU has a memory size of 64MB (!!) to 256MB depending on model type, whereas recent GPUs have 1GB or more).
Let's compare this to a mid-range 3 year old GPU:
Vendor: NVIDIA Corporation
Render: GeForce GTX 550 Ti/PCIe/SSE2
Version: 4.3.0
(...)
Maximum texture size : 16384
Or even a really crappy 3.5 year old GPU:
Vendor: NVIDIA Corporation
Render: GeForce 210/PCIe/SSE2
Version: 3.3.0
Maximum texture size : 8192
Bottom line is that the splash screens are in place, the game can see them:
15 Splashscreens available.
And since this is not followed by any error in the log, the splash screens are loaded fine, but your GPU can't show them due to it's limited capabilities.
I'm sorry to say but we just can't keep each and everything backward compatible for 10 year old hardware, so you'll have to deal with the black screen at game start unless you put your own (smaller) splash screen images in place (instructions given here but it requires some knowledge about IL-2 modding:
https://www.sas1946.com/main/index.php/topic,36163.msg396283.html#msg396283).
Best regards - Mike