what shutter speed u are using? if u are using shutter priority, in day time, u will get dark images possible is bcoz
1) u r shooting against something very bright aka back light
2) your picture consists more white than black maybe about 80% white.. (solution: + exposure compensation)
3) your shutter speed set too high 1/4000?
if during daytime indoor, with ISO let say 200, even u use about 1/60 also wont be enough to expose your subject..

for night time, if u want to get still images when shooting kids playing skateboard,
1) u need around 1/125 or even faster, depends on situation
2) if image too dark, u can either a) increase ISO to the level that u can accept or b) flash..

u can learn slow sync flash too..
http://digital-photography-school.com/slow-sync-flash

slow sync flash example


u got me?