Internal Server Error | How to export posts

Hello,

our Blog works since the last Update from 2.5.1 to 2.6.2 very slowly. Mostly I get “Internal Server Errors”, but the MySQL DB is fine. Now I´ve created a new blog but I can´t import the old posts because the export function in the old blog doesn´t work. The .xml File is always to short so there aren´t all of my posts. I also can´t export via RSS because since the last update the RSS feed hasn´t all the posts in it. I would like to ask if I can export and import posts other way, maybe with the MySQL DB.

Excuse my Englisch, I´m German.
Sincerely
Elias Rawish