I haven't deleted anything yet because (gulp - please don't laugh) I haven't worked out where the cache directory is.

Ok... it looks like your host had some issues and that caused the change - sorry for not spotting that before.

I would suggest that you don't delete anything just yet.

Also you shouldn't randomly set files to be writable as this can cause you security headaches in future. Make sure that anything that doesn't need to be writable doesn't have that option set - particularly for "Others" as this includes everyone on your server!

If you connect your FTP client (i.e. SmartFTP) to your host, you should find a directory/folder called forum. Open that folder, and you'll probably find a load of other files, and probably that cache directory/folder that we're looking for.

If/when you find it, right-click on it and set that to 777. Any files with similar names (e.g. cache.php) are irrelevant and should be left alone!

If you can't find it, try creating a directory called cache and set that to 777.

Been there. It's got...
admin_bans.php
admin_categories.php
admin_forums.php
admin_groups.php
admin_index.php
admin_loader.php
admin_maintenance.php
admin_options.php
admin_permissions.php
admin_ prune.php
admin_ranks.php
admin_reports.php
admin_users.php
config.php
database.sql
delete.php
edit.php
extern.php
footer.php
header.php
head.php
index.php
install.php
login.php
misc.php
moderate.php
post.php
profile.php
userlist.php
viewforum.php
viewtopic.php


... but I made a cache folder and did 777 ... and it worked!! Thank you!!!!!