Index: base/setup/usetup/bootsup.c
===================================================================
--- base/setup/usetup/bootsup.c	(revision 74470)
+++ base/setup/usetup/bootsup.c	(working copy)
@@ -644,6 +644,7 @@
     LARGE_INTEGER FileOffset;
     PUCHAR BootSector;
     ULONG Instruction;
+    WORD BootSectorSignature;
 
     /* Allocate buffer for bootsector */
     BootSector = RtlAllocateHeap(ProcessHeap, 0, SECTORSIZE);
@@ -685,6 +686,8 @@
 
     Instruction = *(PULONG)BootSector;
 
+    BootSectorSignature = *(PWORD)(BootSector + 0x1fe);
+
     /* Free the boot sector */
     RtlFreeHeap(ProcessHeap, 0, BootSector);
 
@@ -691,7 +694,7 @@
     if (!NT_SUCCESS(Status))
         return FALSE; // Status;
 
-    return (Instruction != 0x00000000);
+    return (Instruction != 0x00000000 && BootSectorSignature == 0xaa55);
 }
 
 NTSTATUS
@@ -2250,6 +2253,7 @@
 #ifdef __REACTOS__
     NTSTATUS Status;
     BOOLEAN DoesFreeLdrExist;
+    WCHAR OriginalSystemRootPath[MAX_PATH];
     WCHAR SrcPath[MAX_PATH];
     WCHAR DstPath[MAX_PATH];
 
@@ -2369,11 +2373,17 @@
 
         PWCHAR Section;
         PWCHAR Description;
-        PWCHAR BootDrive;
-        PWCHAR BootPartition;
+        WCHAR BootDrive[4];
+        WCHAR BootPartition[2];
         PWCHAR BootSector;
         PWCHAR BootSectorFileName;
 
+        swprintf(BootDrive,
+                 L"hd%d",
+                 PartitionList->OriginalSystemDisk->DiskNumber);
+        swprintf(BootPartition,
+                 L"%d",
+                 PartitionList->OriginalSystemPartition->PartitionNumber);
         if (DoesFileExist(SystemRootPath->Buffer, L"io.sys") == TRUE ||
             DoesFileExist(SystemRootPath->Buffer, L"msdos.sys") == TRUE)
         {
@@ -2382,8 +2392,6 @@
 
             Section       = L"DOS";
             Description   = L"\"DOS/Windows\"";
-            BootDrive     = L"hd0";
-            BootPartition = L"1";
             BootSector    = L"BOOTSECT.DOS";
 
             BootSectorFileName = L"\\bootsect.dos";
@@ -2396,8 +2404,6 @@
 
             Section       = L"DOS";
             Description   = L"\"FreeDOS\"";
-            BootDrive     = L"hd0";
-            BootPartition = L"1";
             BootSector    = L"BOOTSECT.DOS";
 
             BootSectorFileName = L"\\bootsect.dos";
@@ -2409,8 +2415,6 @@
 
             Section       = L"Unknown";
             Description   = L"\"Unknown Operating System\"";
-            BootDrive     = L"hd0";
-            BootPartition = L"1";
             BootSector    = L"BOOTSECT.OLD";
 
             BootSectorFileName = L"\\bootsect.old";
@@ -2440,8 +2444,14 @@
                 wcscpy(DstPath, SystemRootPath->Buffer);
                 wcscat(DstPath, BootSectorFileName);
 
-                DPRINT1("Save bootsector: %S ==> %S\n", SystemRootPath->Buffer, DstPath);
-                Status = SaveBootSector(SystemRootPath->Buffer, DstPath, SECTORSIZE);
+                /* Create original system partition bootsector path */
+                swprintf(OriginalSystemRootPath,
+                         L"\\Device\\Harddisk%d\\Partition%d",
+                         PartitionList->OriginalSystemDisk->DiskNumber,
+                         PartitionList->OriginalSystemPartition->PartitionNumber);
+
+                DPRINT1("Save bootsector: %S ==> %S\n", OriginalSystemRootPath, DstPath);
+                Status = SaveBootSector(OriginalSystemRootPath, DstPath, SECTORSIZE);
                 if (!NT_SUCCESS(Status))
                 {
                     DPRINT1("SaveBootSector() failed (Status %lx)\n", Status);
@@ -2508,6 +2518,7 @@
 #ifdef __REACTOS__
     NTSTATUS Status;
     BOOLEAN DoesFreeLdrExist;
+    WCHAR OriginalSystemRootPath[MAX_PATH];
     WCHAR SrcPath[MAX_PATH];
     WCHAR DstPath[MAX_PATH];
 
@@ -2575,8 +2586,14 @@
             wcscpy(DstPath, SystemRootPath->Buffer);
             wcscat(DstPath, L"\\bootsect.old");
 
-            DPRINT1("Save bootsector: %S ==> %S\n", SystemRootPath->Buffer, DstPath);
-            Status = SaveBootSector(SystemRootPath->Buffer, DstPath, sizeof(EXT2_BOOTSECTOR));
+            /* Create original system partition bootsector path */
+            swprintf(OriginalSystemRootPath,
+                     L"\\Device\\Harddisk%d\\Partition%d",
+                     PartitionList->OriginalSystemDisk->DiskNumber,
+                     PartitionList->OriginalSystemPartition->PartitionNumber);
+
+            DPRINT1("Save bootsector: %S ==> %S\n", OriginalSystemRootPath, DstPath);
+            Status = SaveBootSector(OriginalSystemRootPath, DstPath, sizeof(EXT2_BOOTSECTOR));
             if (!NT_SUCCESS(Status))
             {
                 DPRINT1("SaveBootSector() failed (Status %lx)\n", Status);