Ok then you have no problem at all

You are currently receiving public service ads.
Google adsense takes a few days to display relevant ads to your site.
Replace my code with your adsense code (you can leave mine if you feel generous

) and wait a few days. The ads will show up over time, depending on the saturation of your keywords.
And make your forum readable for guests. Only this way google can serve you relevant ads.
If you want to take a read on google adsense I would suggest:
http://forums.digitalpoint.com/
This is a great community for webmasters.
Good Luck
StarBuG