Buffer issue

Hi,
I just finished installing my XBMC, and it's the first time I am going to use it.
It's installed on a laptop , Asus Zenbook, Windows 7 64bits, 8Go RAM. ( I am running only XBMC on it)
I tried running an HD Movie, size of the MKV file is 30 Go.
It keeps buffering every 30-40 seconds.
Is there anything on my setup that I need to optimize?
Is the file too big for XBMC?
Is there anything I should look at?
(I did increase the cachemembuffersize to 500Mo to see if it will improve but no improvement).
Thank you.