roll back to 609 from b830

Hi, I updated my phone by manual way with dload folder from b609 to b621 to b623 to b630. Somehow something went wrong. b830 seems to be working but cant conet to te network. cant even change the motive on my phone. tried to roll back to 623 from 830 by simply using dload folder but it does not work. it seems that it downgrades but the soft is still b830. can i roll back to b609? the most important thing is that i can not even do the factory reset. it resets up to about 40 per cent and then the fail appears. when i turn on the phone it looks like it did work becase i have to set the language and the display settings but still cannot connetc with wi fi to the internet. i am hopeless. can i do it in such a way not to loose the guarantee. i think i still have it. i do not want to wait for the phone for a month before it is fixed.