Hi i had the same problem as you it was 'driving me mad' but i got there in the end by doing every that the router said to do & also what i had to do with the psp,(i guess the same as you have done) but what made it work in the end for me was to change the channel on my router (mine was set at 1 so i changed it to channel 10) you have to go into the modem router set up to do that & that seemed to do the job for me!
hope that helps cause i know how frustrating it is
let me know & good luck
kev