PHP through Apache does not work after upgrade

[Rexxars]

Hi!

Encountered a bug in PHP on the server, so I decided to try and upgrade Plesk hoping it would upgrade PHP. Well, something went wrong.

Firstly Apache wouldn't start but I fixed that by remove 'php_admin_value' as mentioned in the log from a config file. But now, Apache won't read interpret PHP files- it just outputs them to the web browser!

Here's the parts from the log that I could tell went wrong:

Purging configuration files for apache2-common ...
dpkg - warning: while removing apache2-common, directory `/etc/apache2/conf.d' not empty so not removed.
dpkg - warning: while removing apache2-common, directory `/var/www' not empty so not removed.
(Reading database ... 45856 files and directories currently installed.)
Preparing to replace apache2-mpm-prefork 2.0.54-5sarge1 (using .../apache2-mpm-prefork_2.2.3-4+etch1_i386.deb) ...
invoke-rc.d: unknown initscript, /etc/init.d/apache2 not found.
dpkg: warning - old pre-removal script returned error exit status 100
dpkg - trying script from the new package instead ...
dpkg: ... it looks like that went OK.

Starting web server (apache2)...Syntax error on line 15 of /var/www/vhosts/<maskedsite>/conf/httpd.include:
Invalid command 'SuexecUserGroup', perhaps misspelled or defined by a module not included in the server configuration
[31mfailed! [39;49m
invoke-rc.d: initscript apache2, action "start" failed.

Trying to establish test connection... connected
done
Syntax error on line 2 of /var/www/vhosts/<maskedsite>/conf/vhost.conf:
Invalid command 'php_admin_value', perhaps misspelled or defined by a module not included in the server configuration
websrvmng: Service /etc/init.d/apache2 failed to reload
websrvmng: Service /etc/init.d/apache2 failed to reload

Also, when I try to upgrade Plesk through the control panel, it now says

Error: Not found source for system packages (release 3.1, codename sarge) in /etc/apt/sources.list

But source.list looks like this:

deb https://autoinstall.plesk.com/debian/PSA_8.1.1 sarge all
#deb http://packages.dotdeb.org stable all
#deb-src http://packages.dotdeb.org stable all

deb http://ftp.de.debian.org/debian/ stable main
deb-src http://ftp.de.debian.org/debian/ stable main

deb http://security.debian.org/ stable/updates main
deb http://www.backports.org/debian/ sarge-backports main contrib non-free
deb-src http://www.backports.org/debian/ sarge-backports main contrib non-free

Any ideas? I'm totally lost and don't know where to turn.