Welcome to the forums

. Between the time it worked and now, did you install anything different or flash anything from recovery or hboot? Have you done anything difference since the time it worked? Let's check a few things:
1) With the phone booted up, go to your app drawer, and find an app called superuser. Assuming it exists, open it up. You'll see a list of allowed app and a list of denied apps. Do you see wifi tether in either list?
2) Install the terminal emulator from the market if you don't already have it. Open it up, and type "su" without quotes, then enter. Does the prompt change from $ to #, or do you get a permission denied error?
3) Turn the phone off, then turn it back on while pressing and holding volume down. That will take you to hboot. Do you see S-ON or S-OFF. This is not entirely dependent on your ROM being rooted, but it'll tell us if unrevoked worked properly.
Let's start with that. There are a few other things to check as well.