What the heck is "short vertical scrollbar"? Do you mean the rectangular part on right scrollbar you click on to scroll up/down? This one changes dimension accordingly the number or rows in used area on sheet.

When this is what you are asking about, then getting it short means, that you really have something entered into some cell way down. Use Ctrl + End to locate last used cell on sheet.
In case it will be on the max allowed column or max allowed row for your Excel version and there is not any real entry, then it means for some column you have defined something what makes Excel to mark all rows used for this column (I have encountered such cases in past, but I din't remember anymore what kind of thing this was. And having it defined for entire row/column means, you can get rid of it only deleting rows/columns fully - otherwise the problem is recreated). When this is the case, then the simplest way to correct it is to create a new sheet, copy all data from range you count the proper one only (values, formulas, formats, etc.) from compromised sheet to new one, and then delete the compromised sheet.
When otherwise, then either clear any info from last cell (e.g. dragging some unused cell over it), or delete all rows (when the last cell was in some column used for your real data) or columns (when the last used cell was in some column to right of any columns used for your real data) from last row/column below/right of your real data until row/column of last used cell your did locate, or until last row/cell of sheet.