Stargate (film)/WMG

If you are referring to something from the TV Series, please say so for the benefit of those who haven't seen the series yet.

Ra is not a Goa'uld
One of the (many) nagging differences between Stargate and the various follow-on series is the depiction of the Goa'uld. In the movie, Ra appears to be a human boy possessed by a Grey alien, while in the series, the Goa'uld are parasitic snake looking things. Perhaps Ra was simply a different kind of alien, and somehow ended up working his way into the Goa'uld's setup. Or maybe he started as a Goa'uld, and was possessed by a different alien in turn, with the two aliens' origin stories being mixed up by the humans on Abydos.
 * Or, the Grey alien was an earlier form of Asgard, and his last host.
 * The RPG says Ra's previous host was indeed an Asgard.
 * IRL: This is just one of many examples of how SG-1's canon disregarded the film. Ra appears briefly in Continuum, played by a different actor and is a Goa'uld system lord just like any other.

Ra's exploding spaceship sent out an energy wave that filled the power cells for the gate, enabling the team to dial home.
This is a reaction to the very good Headscratchers question "How did they dial the gate from the Abydos side?". Unbeknownst to them they lucked out with this. There was just enough charge in it dial once.

The movie and the TV series are in slightly different alternate realities.
Stargate SG 1 allows for alternate realities - several shows have touched on this. This neatly explains the differences between the movie and the resulting series.