I'm having so many problems with my new N900 that Nokia sent to me as a REPLACEMENT. First were the apps now whenever I open a threaded message from someone it's completely blank showing nothing what they or what I have said. Can someone help me fix this problem?

Turn off the phone and turn on - the messages will be there again.

Let us know which apps do you have installed - comparing the lists can let us find the one which causes the problem.

I just installed Hermes and even that doesn't sync all my contacts. I already tried turning it off and back on, hasn't worked

So it is another problem. Mine looks like the conversation app freezing. After reopening, whole conversation list is completely empty. Maybe it is blocked by the frozen process, so turning the N900 off/on helps.
In your case, you see the list of conversations but cannot successfully open an existing thread. I suppose you've tried uninstaling Hermes...