Where do I go from here???

I have found my great grandfather Olaf Martinsen on the 1865 census & I see that he had 2 older brothers. 1865 census I also found his brothers & an uncle & his father on the 1900 census. I don't know where to go from here. I can't find his father, Martin Jørgensen or his uncle Ole on early censuses. Is the digital arkivet the only place has the censues? Are there earlier or later ones online? I would like to know what happened to his brothers Jens & Johan & I would love to trace my family back further than my great great grandfather. I have gone to the LDS website & I haven't been able to find anything there either. This is what I know, my great grandfather Olaf Martinsen was born February 05, 1857 in Borge, Fredrikstad, Østfold, Norway. His parents were Martin Jørgensen, born abt 1819 & Enger Oline Jensdatter, born about 1815. I believe his parents were also born in Borge, Fredrikstad, Østfold, Norway. He had 2 older brothers, Jens (abt 1851) & Johan (abt 1848). Any advice or help would be greatly appreciated. Thank you! [:)]