what to do

Well by definition beating everything means there is nothing left to beat. So all you are left to do is catch Pokemon and try to develop the strongest team possible and see how well they do. I find it very difficult to believe you have beaten everything. Have you caught all the pokemon? Beaten tower tycoon palmer twice, to get the gold? Trust me there is so much you could be doing in this game that there is no way you have beaten everything, if you can't find anything new to do either give your game to someone or re start brand new and try things a little bit differently

Depends what you mean by 'everything'. If you've gotten the black trainer card, then you've completed nearly everything you can do on Diamond and Pearl. If you don't have it, continue doing all the objectives to get the black trainer card. When you've completed that, all that's left to do is keep training all the Pokemon you have, and make the best team you can make.

Hope this helps,
Sk8rboy

Well you should try to catch all the Pokemon there is and get them to level 100 then you could have the ultimate team hoped this helped Dominik101 out.

I don't beleive you. You've probly thought you've beaten everything but you haven't.

All you can do is make a stronger team, and battle people.

Hope this helps.

Catch every Pokemon or fill up your pokedex