为什么g++不起作用

我正在使用MinGW，每当我试图从命令行运行g++时，我都会收到以下弹出错误：

由于找不到libgmp-10.dll，此应用程序无法启动。重新安装应用程序可能会解决此问题。

我检查了一下，发现MinGW/bin中实际上有一个名为libgmp-10.dll的文件。起初没有，但我下载了文件并放在那里。MinGW/bin一定不是放置它的正确位置，因为它仍然表示找不到文件。

那么我该把libgmp-10.dll放在哪里呢？

更新：这是我的PATH环境变量：

C:MinGWbin:
/c/Program Files/Vim/vim74:
/c/Program Files/Haskell/bin:
/c/Program Files/Haskell Platform/2013.2.0.0/lib/extralibs/bin:
/c/Program Files/Haskell Platform/2013.2.0.0/bin:
/c/WINDOWS/system32:
/c/WINDOWS:
/c/WINDOWS/System32/Wbem:
/c/Program Files/QuickTime/QTSystem/:
/c/Program Files/TortoiseHg/:
/c/Program Files/Haskell Platform/2013.2.0.0/mingw/bin:
/c/Program Files/nodejs/:
/c/sbcl:
/c/emacs/bin:
/c/Documents and Settings/[my name]/Application Data/cabal/bin:
/c/Documents and Settings/[my name]/Application Data/npm:
.f

这是MinGW:的内容

/MinGW
    /bin
    /include
    /libexec
    /msys
    /var
    /doc
    /lib
    /mingw32
    /share

这在MinGW/bin:内部

aclocal          autoreconf-2.68  ld.exe                    msgcat.exe
aclocal-1.10     autoscan         libcharset-1.dll          msgcmp.exe
aclocal-1.11     autoscan-2.13    libexpat-1.dll            msgcomm.exe
aclocal-1.4      autoscan-2.68    libgcc_s_dw2-1.dll        msgconv.exe
aclocal-1.5      autoupdate       libgettextlib-0-18-3.dll  msgen.exe
aclocal-1.6      autoupdate-2.13  libgettextpo-0.dll        msgexec.exe
aclocal-1.7      autoupdate-2.68  libgettextsrc-0-18-3.dll  msgfilter.exe
aclocal-1.8      c++.exe          libgmp-10.dll             msgfmt.exe
aclocal-1.9      c++filt.exe      libgmpxx-4.dll            msggrep.exe
addr2line.exe    cc.exe           libgomp-1.dll             msginit.exe
ar.exe           cpp.exe          libiconv-2.dll            msgmerge.exe
as.exe           dlltool.exe      libintl-8.dll             msgunfmt.exe
autoconf         dllwrap.exe      libltdl-7.dll             msguniq.exe
autoconf-2.13    elfedit.exe      libmpc-3.dll              ngettext.exe
autoconf-2.68    envsubst.exe     libmpfr-4.dll             nm.exe
autoheader       g++.exe          libquadmath-0.dll         objcopy.exe
autoheader-2.13  gcc-ar.exe       libssp-0.dll              objdump.exe
autoheader-2.68  gcc-nm.exe       libstdc++-6.dll           pthreadGC2.dll
autom4te         gcc-ranlib.exe   libtool                   pthreadGCE2.dll
autom4te-2.68    gcc.exe          libtoolize                ranlib.exe
automake         gcov.exe         mingw-get.exe             readelf.exe
automake-1.10    gdb.exe          mingw32-c++.exe           recode-sr-latin.exe
automake-1.11    gdbserver.exe    mingw32-cc.exe            size.exe
automake-1.4     gettext.exe      mingw32-g++.exe           strings.exe
automake-1.5     gettext.sh       mingw32-gcc-4.8.1.exe     strip.exe
automake-1.6     gettextize       mingw32-gcc-ar.exe        windmc.exe
automake-1.7     gprof.exe        mingw32-gcc-nm.exe        windres.exe
automake-1.8     iconv.exe        mingw32-gcc-ranlib.exe    xgettext.exe
automake-1.9     ifnames          mingw32-gcc.exe           zlib1.dll
autopoint        ifnames-2.13     mingw32-make.exe
autoreconf       ifnames-2.68     mingwm10.dll
autoreconf-2.13  ld.bfd.exe       msgattrib.exe