;I am aware of the missing linker settings / includes..ect, thats not the problem.
.Data

szAlphabet  DB 'abcdefghijklmnopqrstuvwxyz', 0
randbuff    DB 6 Dup(0)

.Code

start:
    Lea Edi, [randbuff]
    Mov Ebx, 0
@@:     Cmp Ebx, 5
        Je done
        Call GetTickCount
    Xor Ecx, Ecx
    Inc Ecx
    mul ecx
    add eax, 7
    Mov Ecx, 24 ;letters in the alphabet
    Sub Ecx, 1
    inc ecx
    xor edx, edx
    div ecx
    Add Edx, 1
    Mov Eax, Edx
    Mov Al, [szAlphabet + Eax]
        Mov Byte Ptr [Edi + Ebx], Al
        Inc Ebx
        Jmp @B
done:


Invoke MessageBox, NULL, Offset randbuff, NULL, MB_OK
Invoke ExitProcess, 0

end start