When I try to open Edit in Sharepoint Designer I get a message that says
"Sorry, the page you're looking for can't be found"
and then I get a window security asking me for username and password, when I enter username and password then a document in Word open very strange.
I have tried another colleague computer and she can open it without any problem.
How do I solve the problem?
We work with SharePoint 2010 and I experienced the same problems with SharePoint Designer 2010 (SPD). I didn't open the site or the page but it was installed. This is caused by two problems.
First being the fact that IE doesn't recognize that SPD is installed, IE11 in this case. In my case it was caused by an update to Office 2013, apparently a series of Add-ons was changed. A simple reinstall of SPD fixed this problem.
Because IE doesn't see SPD it redirects you to the download page via a hard-coded link which can be found in core.js files of your SharePoint intallation. This link goes to this new download link. This link returns a header with the following setting: X-Frame-Options:SAMEORIGIN and thus is not allowed to be shown in an iFrame. Download and install SPD manually.
Have you enabled SPD on your Web Application in Central Administration, and have you enabled the use of SPD on the site collection your wording on, and have you at least design permission on the site you want to edit?
Reference: Manage Permissions and Control Access to Sharepoint Designer
