the Dragon balls didn't work because do to the fact the androids had killed piccolo which causes Kami to die along with him which turned them into stone and can't no longer work.
The only reason future Trunks didn't use the dragonballs to bring his friends back to life is because piccolo had died and it is told that if piccolo dies the earth's dragonballs are worthless
There is no information given in the series about what happened to them prior to the Dragonball Manga/anime. However, the first wish made on the Dragonballs in the series was Oolong who wished for "the panties from a real hot girl".
On Earth, Kami created the Dragonballs. On Namek, the Namekian elder created them. When the person who created the dragonballs dies, the dragonballs disappear. This is why, after Kami dies, Dende replaces him as guardian of Earth and creates a new set of Dragonballs.
There are 7 dragonballs. If you are reffering to the manga there are 16 volumes.
No everyone remains dead apart from Trunks and Bulma.
Go to dragon history and crash through things while fighting . You still have to win though.
Online or in stores
In Dbz it is goten, but in the dbz movie history of future trunks its gohan cause since goku got sick goten was never born and gohan was trunks' mentor!
In the TV special 'The History of Trunks'.
Gohan lost his arm by saving trunks from the androids,that was depressing it got blew up by the blast in History of Trunks
Unfortunately, you can't
Emperor Pilaf got a hold of the Dragonballs but then adult Goku stopped him before anything bad happened. So Emperor Pilaf wished he was a kid and it Happened!