problems loading certian webpages

Alright...here goes nothing, so...like an idiot i listened to my bud and downloaded hijack this, clicked everything it scanned and clicked fix button...made a backup folder with all files in it and whatnot, but now when i try to go to a website like mail.yahoo.com or paypal.com i get an error message saying i can't be connected cuz server can't be found, but its only on websites like that...myspace works, all other websites seem to work, only ones i've found problems with so far is paypal and any e-mail pages where you type in password and username...can anyone offer me a bit of advice other than not listening to my (apparently, unless he was right ) stupid friend? :major