Ok fixed the problem. I have no idea how but some settings must have changed when I upgraded. Opened settings->reading and changed the frontpage and posts to correct ones.
Why this happened I still don’t know. I never touched those settings before.
Thanks a lot Chris,
Your explanation cleared a lot of things. However, I was unable to place any flash in the place of slideshow so I duplicated header.php, renamed it header_new.php and modified it instead cause that’s the part where the slideshow code really is. I was wondering if there was a more elegant solution.
Anyways thanks a lot again