Whole package suddenly broken

[benFF]

For some reason, the links directory has suddenly just stopped working giving 500 errors on every page.

PHP log shows: [01-Mar-2012 21:50:03] PHP Fatal error: Using $this when not in object context in W:\Domains\xxx.com\wwwroot\includes\class_hook.php on line 57

I bought an upgrade to the latest version but still no dice.

As far as I'm aware, nothing has been changed on the system - it just suddenly started doing it!

[Brian]

I can't say I've heard of an error like that before... I'd suggest disabling all other products/plugins and see if you still have the same issue. If not, then you can start re-enabling them one by one to figure out what's causing the issue.