Can not edit or create new pages

After installing e-commerce, every thing worked find that day. the next day, I am not able to edit or create new pages. When I try to create a new page and click preview or submit, all data is erased and it is at the point as if I juct clicked to add a new page. If I edit a page, no matter which button I select, that status doesn't change. My site is www.swailsnet.net. Any suggestion would be appreciated.