I pasted a lot of data in Column A.
Then I removed duplicates:
Data > Filter > Standard Filter > More Options > No Duplication
Now I'm stuck in row 2632, i.e. I can´t scroll up to rows above 2632.
What's my issue?
It sounds like you accidentally hide your cells. If you select all the cells by clicking in the little blank area in the top left, (or press Ctrl-A) then right click on a number and click Show your data should re-appear.