Make sure all the required ports on your router are open or your PS3 is sat in your routers DMZ (the option I go for) and you should be OK.
I know I had to do a hard reset on my router before I could set-up or join any lobbies, so that may be worth a go as well.
BTW - The AUP here at GT Planet requires that you use good basic grammar when posting. That includes using capital letters for the start of sentences, nouns and single 'I's.
Please ensure that all your posts follow the AUP.
Regards
Scaff