Canon rebel t3i captures dark images when the flash is on.

good day!!!

my canon rebel t3i captures dark images when the flash is on, and sometimes it produce totally balck image. but when the flash is off it produce a good normal images.

in other scenario sometimes the image went well with flash on. this only if i capture a continuous and non stop photos.

without flash

flash on with dark image result

flash on with normal result

thank you.