Error during installation – index.php problem

Kind of a long story how I got to this point – and I’ll be the first to admit when it comes to this – I know just enough to be dangerous. However, here’s the situation:
I have to rebuild the files for this blog. But since there are numerous entries, uploads etc. I don’t want to rebuild the database.

This is the error I am now receiving

Fatal error: Call to undefined function: get_header() in /home/mydatabase/wordpress/index.php on line 1

Any recommendations would be greatly appreciated.