Floating-point operations in MASM32

Question

So, I have a code, in which I'm calculating a/b-d*c. Separately, it works just fine, but if I'm trying to put it into my project code, I'm getting "f" or "0.0e..." after calculations.

.686 
.MMX
.model flat, stdcall 
option casemap:none 
include \masm32\include\windows.inc ; 
include \MASM32\INCLUDE\masm32.inc
include \masm32\macros\macros.asm
uselib user32, kernel32, masm32, fpu
.data
_a dd 10.0
_b dd 3.0
_c dd 2.0
_d dd 5.0
res REAL8 ?
buf1 db 255 dup(?) ; 
array1 DWORD 1, 5, 15, -15
array2 DWORD 2, 4, 16, 16
result DWORD 0, 0, 0, 0 ; xor result array
MaxResult DWORD 4 dup(?); max elements array
maxIndex DWORD ?
pxorStr db "PXOR: %d, %d, %d, %d", 0
maxStr db "Max values of arrays: %d, %d, %d, %d", 0 
calcStr db "Calculation result: %f", 0
tit1 db "Result of using the MMX", 0
.code
start:
    mov esi, offset array1
    mov edi, offset array2
    mov ebx, offset result
    mov ecx, 4
    pxor_loop:
        movq MM0, [esi]
        pxor MM0, [edi]
        movq [ebx], MM0
        add esi, 4
        add edi, 4
        add ebx, 4
        loop pxor_loop
    ; Check third element and determine max elements if it <15
    mov eax, DWORD PTR [result+8]
    cmp eax, 15
    jle MaxElements
    mov eax, DWORD PTR [result+12]
    cmp eax, 0
    jge Calc1
    jmp Calc2
MaxElements:
;create array of max elements
    mov ecx, LENGTHOF array1 ; loop counter
    mov esi, OFFSET array1 ; source array 1
    mov edi, OFFSET array2 ; source array 2
    lea ebx, MaxResult ; destination array
    mov maxIndex, 0
compareLoop:
    mov eax, DWORD PTR [esi]
    mov edx, DWORD PTR [edi]
    cmp eax, edx
    jge a_greater_b
    mov eax, edx
a_greater_b:
    mov DWORD PTR [ebx], eax ; store max element
    add esi, TYPE array1 ; increment pointer to source array 1
    add edi, TYPE array2 ; increment pointer to source array 2
    add ebx, TYPE MaxResult ; increment pointer to destination array
    inc maxIndex ; increment index
    loop compareLoop
        
Calc1:
;a/b-d*c
    fld _a
    fdiv _b
    fld _d
    fmul _c
    fsubp st(1), st(0)
    fstp res
    jmp DisplayResult
    
Calc2:
;a/b
    fld _a
    fdiv _b
    fstp res
DisplayResult:
; Display results in message box
    invoke wsprintf, ADDR buf1, ADDR pxorStr, DWORD PTR [result], DWORD PTR [result+4], DWORD PTR [result+8], DWORD PTR [result+12] ;for xor
    invoke MessageBox, 0, addr buf1, addr tit1, MB_OK
    invoke wsprintf, ADDR buf1, ADDR maxStr, DWORD PTR [MaxResult], DWORD PTR [MaxResult+4], DWORD PTR [MaxResult+8], DWORD PTR [MaxResult+12];max res
    invoke MessageBox, 0, addr buf1, addr tit1, MB_OK
    invoke FloatToStr, res, OFFSET buf1;calc
    invoke MessageBox, 0, OFFSET buf1, addr tit1, MB_OK
    invoke ExitProcess, 0
end start

Problem are in function Calc1/Calc2 and FloatToStr function. I guess that's because MMX commands here, but it's part of a task, so I can't re-do it without it.

I've tried to use fptoa function before, but it didn't work at all, so I've choosed FloatToStr one.