To find a version for your pc check with the software publisher install mongodb
Which version did you download and install?  If you have 64-bit Windows 8, you should download and install the build marked with "2008R2+".  Their download page indicates that:


  The Windows 2008+ build uses newer features of Windows to enhance
  performance. Use this build if you are running with 64-bit Windows
  Server 2008 R2, Windows 7, or greater.


If you are using 32-bit Windows 8, you should download the 32-bit Windows version.  Of course the 32-bit version has some limitations, such as a max database size of 2GB.