Category box disapeared and other errors

[FireHawk]

I am very new to this and have recently just been playing around trying to understand how it all works before uploading catagories/products via csv.
Everything was working fine and i was understanding how to lay things out nicely.
Got round to looking at uploading a short csv file to try to add 3 categories.
Had a few errors uploading due to me not filling in urls etc as i didn't want any pictures as yet as i was still trying to learn how it's all done.
It added the categories, not quite as i expected but i think i know where i went wrong there now.
After going in to delete them manually, it always leaves one subcategory behind, even though it says deleted. Sometimes i get an "internal server error" too.

I am ready to throw the towel in so any advice would be greatly appreciated.
I am thinking of deleting the whole prestahop from my hosting and trying for a fresh install.

Regards

Chris