I'm with trouble trying to open a specific extensions (I want to open *xls)

I have currently this code:

import os 
os.system('C:\\file.bmp') # this works, and opens the file
os.system('C:\\file.xls') # this doesn't work.

In specific extensions (like xls) The OpenERP freezes completely on "loading...", and most of the times, it makes me reboot computer because the "localhost:8069" becomes totally unavailable. Not even restarting the service openERP works.

Any ideas?