Depends what mission your stuck on. Go on halopedia they have walkthroughs of ever single mission
I am not sure if skulls are on the screen means that you have beat the campaign. It usually just means that you have beat the mission.
Of course
About 2 or 3 days.
It depends which Halo and which Fable. If you mean Halo 1 vs. Fable 1, then I'd say Fable, because Halo 1 doesn't have multiplayer on the Xbox. But, if you mean Halo 3 vs. Fable 2, then I personally like Halo 3 better. Halo 3, even after you beat the campaign, the game has longevity because there is multiplayer, whereas once you beat the Fable campaign, you're bored with it.
beat campaign on legendary
beat the campaign on heroic(might as well beat it on legendary),and go on halo waypoint(u need xbox live)
Unlock Halo 3:ODST's Campaign Complete Achievement. Once you beat the ODST campaign, visit Halo Waypoint on the dashboard to unlock the item.
Finish the Halo 2 single player campaign.
It depends on what you call beat. To Complete Halo you should complete All Campaign missions, Some people also may want to try it on harder difficulty levels. There are also some skull you could find
Be player 2 in the halo 3 co-op campaign. Or, play the Arbiter levels in halo 2.
To beat the campaign mode, play through all the levels, follow the story's instructions, and don't die.
I'll help you complete campaign I have beat it before my gamertag is CSI kid