ImportError: No module named 'numpy' while installing scikit-learn

I am trying to test scikit-learn library, but didn’t manage to install it.

More details : I did install numpy, scipy, matplotlib and I can use them just fine. However, when I use pip (pip install -U scikit-learn), I get this error :

Partial import of sklearn during the build process.
Traceback (most recent call last):
    File "<string>", line 1, in <module>
    File "C:Users...scikit-learnsetup.py", setup_package()
    File "C:Users...scikit-learnsetup.py", from numpy.distutils.core import setup
ImportError: No module named 'numpy'

I couldn’t find anything about this.

I tried installing scikit-learn directly by using python setup.py and had the same problem. Any ideas?