another fatal error topic & some.

Fatal error: Call to undefined function: get_header() in /home/sagic/public_html/wp/wp-content/themes/lavazza800/index.php on line 1

I’ve made a new theme and I try to access the index page of it and I get this error.
I recently installed the theme switcher plugin and I’ve suddenly gotten an error at the top of my admin panel:

Warning: Cannot modify header information – headers already sent by (output started at /home/sagic/public_html/wp/wp-content/plugins/theme-switcher.php:2) in /home/sagic/public_html/wp/wp-admin/admin.php on line 10

Warning: Cannot modify header information – headers already sent by (output started at /home/sagic/public_html/wp/wp-content/plugins/theme-switcher.php:2) in /home/sagic/public_html/wp/wp-admin/admin.php on line 11

Warning: Cannot modify header information – headers already sent by (output started at /home/sagic/public_html/wp/wp-content/plugins/theme-switcher.php:2) in /home/sagic/public_html/wp/wp-admin/admin.php on line 12

Warning: Cannot modify header information – headers already sent by (output started at /home/sagic/public_html/wp/wp-content/plugins/theme-switcher.php:2) in /home/sagic/public_html/wp/wp-admin/admin.php on line 13

Warning: Cannot modify header information – headers already sent by (output started at /home/sagic/public_html/wp/wp-content/plugins/theme-switcher.php:2) in /home/sagic/public_html/wp/wp-admin/themes.php on line 18

could that have something to do with my index error?