Lines like tables suddenly appeared on my whole document while I was away from it for a few days. How do I get rid of them? Please help. Thanks.
Please provide more information, Ask/Guide - How to use the Ask site - The Document Foundation Wiki
[Edit]
Try this, right click on the offending page and select Page style. In the dialogue, select the Text Grid tab and choose No grid (default for Western) or if you need the grid, untick Display grid
It could be sections:
The Navigator (F5) also could help here.