Cannot scroll up the page.

There are few possibilities as to why this is happening:

1. The rows above row 298 have been hidden. You will need to unhide the rows to resolve this.
2. The panes are frozen (understand that you have explored this already).
3. The rows above 298 have been grouped together. You will need to click on the "+" signs on the extreme left.

Do let me know if these solutions work for you.