Facebook

[supapapa]

I tried to block an advert on Facebook but ended up blocking everything, how do I get it back please?

[Buenchico]

How did you try to block the ad? Was it with, for example, something like Adblock Plus or was it in another way?

If it was with Adblock Plus you need to be aware that there's a MASSIVE battle going on between Facebook and Adblock Plus which has resulted in Facebook making ads part of the same page as Facebook posts (rather than having them provided by an external server, as AB does) in an attempt to render Adblock Plus totally ineffective:
http://www.bbc.co.uk/news/technology-37056013
(AdBlock Plus has had to defend court battles in several countries from website owners who want to see their software totally banned).

How you reverse a block in Adblock Plus might depend upon which browser you're using. The following is for Firefox (but it might still apply elsewhere):

Go to the relevant page.
Click the 'ABP' logo at the top right.
Click 'Open blockable items'
Scroll down the list to find the relevant item. (Hint: If you hover your mouse over a line it will show the source of the blocking instruction against 'Filter source'. Assuming you're using the default blocking list, most will show 'EasyList' but you're looking for an entry which shows that you chose to block it yourself).
When you've found it, right-click and select 'Disable filter'.

[supapapa]

Thank you I have sorted it now.