Follow this guide:
http://wiki.maemo.org/Updating_the_f...ndows_7_32-bit

(I would advise to leave "-R" away when flashing fiasco because it just makes device reboot and actually we do not want it when we are going to next flash emmc)

So
- First flash your fiasco (you did this already but do it again), without -R switch in the end
(Please understand that flashing vanilla makes all your messages and contacts disappear from your N900, only stuff what is on your Sim car will stay)
- Follow guide and download Vanilla image from same place where you downloaded your fiasco image
- Run flasher as advised in guide. (filenames for images might be different but leave switches)
- Device should reboot