After an second attempt and failing on it, i've found the solution. It isn't that hard to do.
First you have to determine the id of the extension that has changed the new tab. You do that to go to the extensions -> then go in development mode -> and then you see the ID's.
After that, go to the chrome default folder (C:\Users\user-name\AppData\Local\Google\Chrome\User Data\Default ) and copy (for backup) the file Preferences
Now close chrome, and open the file Preferences in any texteditor.
Search the file for something like this:
"newtab": [ "chrome-extension://aaaangaohdajkgeopjhpbnlpkehbhmbj/config/skin/new-tab.html" ]
NOTE! the ID is probably difrent, but it has to be something like this :
Now look further down for "settings" and then the id of your extension.
There will be again somekind of this line:
Delete that one to.
Save the file and start chrome and it will be fixed.