Upgraded to 2.3.1 using fantastico now nothing works!

Argh! I have never upgraded my wordpress before and had no clue how to do it, so I used Fantastico.

Firstly, I got this error msg:

WordPress database error: [Table 'twistsol_wrdp1.wp_post2cat' doesn't exist]
SELECT SQL_CALC_FOUND_ROWS DISTINCT wp_posts.* FROM wp_posts LEFT JOIN wp_post2cat ON ( wp_posts.ID = wp_post2cat.post_id) WHERE 1=1 AND post_type = 'post' AND (post_status = 'publish' OR post_status = 'private') AND wp_post2cat.category_id NOT IN (7) ORDER BY post_date DESC LIMIT 0, 1

And a similar one for my Sideblog plug in:

WordPress database error: [Table 'twistsol_wrdp1.wp_categories' doesn't exist]
SELECT cat_ID FROM wp_categories WHERE category_nicename='sideblog'
Aside category not selected

(Yes I am going to upgrade it soon!) So I disabled all the plug ins I am using and now I get this message:

Fatal error: Call to undefined function: sideblog() in /home/twistsol/public_html/wp-content/themes/OldWallpaper/sidebar.php on line 11

…that’s it, just that – the rest of the layout has gone:

https://twisted-solutions.co.uk/ – see!

If I upgrade the plug-in will that fix the entire problem…? Is there anything I need to do?

Sorry If I’m a pain in the bum!