Having forum trouble

For like the last couple of months forums on my computer been acting strange. When there say 30+ posts in a thread and I go to look at it, it'll only show me the first 10-20 posts/let me only go as far as the second page of posts even if there over 100 reply's. There also a ...i guess a text box(?) above the thread that lists individual posts and lets me "go below current depth" but even that only lets me see a few additional posts. Anyone else have this problem and know how to fix it? would like to be able to read longer threads.