404 Not Found The requested URL does not exist.

I just upgraded to 2.6.2 from a very old version (2.0 probably). I had the login error and resolved that by renaming my plugins folder. It asked me to do the database upgrade after that.

Now, my blog will come up but no posts or pages can be clicked on. It gives me:

404 Not Found
The requested URL does not exist.

When I try to save a new page or post it gives me this error:

Warning: fopen(/home/theworl5/public_html/marketability/index.php/.htaccess) [function.fopen]: failed to open stream: Not a directory in /home/theworl5/public_html/marketability/wp-admin/includes/misc.php on line 45

Warning: fwrite(): supplied argument is not a valid stream resource in /home/theworl5/public_html/marketability/wp-admin/includes/misc.php on line 70

Warning: fwrite(): supplied argument is not a valid stream resource in /home/theworl5/public_html/marketability/wp-admin/includes/misc.php on line 72

Warning: fwrite(): supplied argument is not a valid stream resource in /home/theworl5/public_html/marketability/wp-admin/includes/misc.php on line 72

Warning: fwrite(): supplied argument is not a valid stream resource in /home/theworl5/public_html/marketability/wp-admin/includes/misc.php on line 72

Warning: fwrite(): supplied argument is not a valid stream resource in /home/theworl5/public_html/marketability/wp-admin/includes/misc.php on line 72

Warning: fwrite(): supplied argument is not a valid stream resource in /home/theworl5/public_html/marketability/wp-admin/includes/misc.php on line 72

Warning: fwrite(): supplied argument is not a valid stream resource in /home/theworl5/public_html/marketability/wp-admin/includes/misc.php on line 72

Warning: fwrite(): supplied argument is not a valid stream resource in /home/theworl5/public_html/marketability/wp-admin/includes/misc.php on line 72

Warning: fwrite(): supplied argument is not a valid stream resource in /home/theworl5/public_html/marketability/wp-admin/includes/misc.php on line 72

Warning: fwrite(): supplied argument is not a valid stream resource in /home/theworl5/public_html/marketability/wp-admin/includes/misc.php on line 73

Warning: fclose(): supplied argument is not a valid stream resource in /home/theworl5/public_html/marketability/wp-admin/includes/misc.php on line 75

Warning: Cannot modify header information – headers already sent by (output started at /home/theworl5/public_html/marketability/wp-admin/includes/misc.php:45) in /home/theworl5/public_html/marketability/wp-includes/pluggable.php on line 770

Any help provided will be much appreciated.