next / prev links not working

Hi guys, I’m having trouble getting my pages to link up via next / previous links.

Right now when I click on the next/previous posts links (little black banners just above the footer – see here http://tinyurl.com/3g8us5t) I’m taken to single.php with no way back or forwards. I’m using the following for my next / prev
posts code on index.php:

http://pastebin.com/9sDSnHV6

I’m also having problems with my other templates, I have a feeling they can be remedied simply enough but I’ve been scratching my head for a while, having little success on Google and could do with some guidance.
Right now the archives pages change the dates of the posts when you click on eg “july 2011” and but the posts themselves do not change between months, also the categories and tags are not pulling in the correct info (widgets with links are in the sidebar – http://tinyurl.com/3g8us5t).

Here’s my code for the index, single, archive and category pages:

index.php
http://pastebin.com/ZrPHKdAC

single.php
http://pastebin.com/feKZBuLj

archive.php
http://pastebin.com/MTwK9S9w

category.php
http://pastebin.com/1UBeuXR0

Any help would be greatly appreciated!