Cant log into my localhost wordpress site anymore… help plz! :(

hi everyone!
im using MAMP for mac and i actually just downloaded everything, basically starting from scratch (and without knowing much about codes etc…). so actually everything went fine with the installation and i got wordpress to work and even managed to download a theme… but(!) did a stupid mistake.
i just “tried” to change the link/address of the blog from the localhost(8888) to a basic (www.bla—.com) sites address where my old blog from wordpress.com is located.
so yeah, i thought that might be a good idea to try that out and see what happens. after i was redirected to my wordpress.com account and thats it. now, whenever i try opening my localhost server, of course, nothing will open! i tryed reinstalling everything and so, but looks like, ive failed! anyways… please help me out here! first lesson ive learned today: no experimenting! ^^ do i need to change something somewhere? im sure i do… but what and where? i would really need some help! i dont want it to be over before i even started yet 🙁
thanks in advance!