If, for any reason, the oleh stops and is not able to finish his aliya – someone else should be called up to begin again from where he began, with his own beracha before and after. The replacement should not repeat Borchu. (ShA 1 – MB 3)
If you said the beracha before the kria and spoke even one word in any language before you began reading, you will need to repeat the beracha. (MB 6)
If the subject of your interruption pertained to the kria, b’dieved you do not need to repeat the beracha. (MB 6)
It is forbidden to interrupt even with divray Torah in the middle of the kria, even if you do not distract your mind from the kria. (MB 7)
As long as you read at least one possuk before the interruption, you do not have to repeat the beracha. (ShA 2 – MB 6,7)
When reciting the first beracha, it is proper to have in mind that it should cover any reading – even if you need to read more after having hessech hadaas. (Compare: stopped too early – then continued only after being corrected.) (MB 7)
If they showed you the wrong place to begin your aliya, your beracha will cover any pessukim that are open before you – even a different parsha, different column, above or below from where they showed you. (MB 9)
If they showed the wrong place to the oleh and they need to roll the sefer Torah to the right place – do not protest if the oleh does not want to say another beracha, as long as it is from the same sidra of the week. (MB 9)