Keybourdinput (Windows): simultaneosly pressed keys

I am making some mini-spaceshooter-game like Galaga. My problem are the simultaneously pressed keys - the controls are:
WSAD for ship movement and SPACE for fire. Alternative contorls for ship movement are the arrowkeys. If i am using WSAD and SPACE it is all right - you can "fly" and fire. But with the arrowkeys i have some problems: i can "fly" and fire when pressing UP and RHIGHT (and SPACE of course), but not pressing UP+LEFT oder DOWN+LEFT/RIGHT. Searching google and some forums (win32asm and masm forum) for hours and days, i variate my code - from "GetKeyState" about "GetAsyncKeyState" until processing WM_KEYUP/DOWN in the WinMsgProc. At last, i wanted to use DirectInput and see this example: http://www.wasm.ru/forum/viewtopic.php?id=15166. This small program shows me the pressed keys - and getting the input throught DirectInput. But there i can not press all the keys (the below keys) - so my question:

is this DirectInput example correkt and my keyboard is the problem (hardware)? I mean if i use the Control-Key insteat the space-key, it is all right. Using numpadkeys (8,4,5,6 +SPACE) - the same problem. Using numpadkeys (8,4,2,6) works too.

or have i some error in reasoning?

You can answer me in russian, too - i can read it (but not type it down )

Some code (the Msg Loop):

Код (Text):

1. StartLoop:
2.       invoke TranslateMessage, ADDR msg         ; translate any keystrokes
3.        
4.        invoke GetAsyncKeyState,VK_SPACE
5.        test eax, 80000000h    
6.        lea esi,keystate
7.        .if eax        
8.           mov byte ptr [esi+VK_SPACE],TRUE
9.        .else
10.             mov byte ptr [esi+VK_SPACE],FALSE
11.        
12.        .endif
13.  
14. ;   and so on - i cut this piece of code
15. ;this ist another variation: keystate ist a 256 Byte Buffer  
16.       comment $
17.       .if msg.message==WM_KEYDOWN
18.         lea esi,keystate
19.        add esi,msg.wParam
20.         mov byte ptr [esi],TRUE
21.        
22.        .elseif msg.message==WM_KEYUP   
23.         lea esi,keystate
24.         add esi,msg.wParam
25.         mov byte ptr [esi],FALSE
26.       .endif
27.       $
28.       invoke DispatchMessage,  ADDR msg         ; dispatch the message to the WndProc
29.     jumpin:
30.       invoke GetMessage,ADDR msg,NULL,0,0       ; fill the MSG structure
31.       test eax, eax                             ; test its return value
32.       jne StartLoop                             ; loop back if its not ZERO

 

I almost on 100 % am confident that Dinput example is correct. Different keyboards have hardware restrictions on the certain combinations of keys pressed simultaneously. It is desirable to not use such combinations.