When you're reading a post...You'll see:
zIWETHEY Home | IWETHEY Board | Suggestions
Then under that, it'll say either:
Show One Comment Only
Or:
Show All Replies
You probably inadvertently clicked the "Show One Comment Only" link once upon a time. This auto-changes your preferences. If you did once click "Show One Comment Only" then your text in the position mentioned above should read "Show All Replies" -- click that, and you should be back to normal.