To re-activate an 8 sheet poster unit (that's what they're called), is more complicated than it looks. I would suggest you buy my book "Big Profits From Big Signs" because it is cheap and teaches you way more information than I could post here. It's available here on the site. But here are some of the highlights of what you need to do:
1) make sure you can legally operate the sign(s). Does it have a permit and do you need a license in your market?
2) comp the other 8-sheet ads in your area to determine a fair asking price.
3) have someone inspect it to make sure it is safe.
4) get pricing to produce the ads, and a template of how they'll get installed.
5) market the ad space as I show in the book.
6) maintain the business as I show in the book.
There is no reason why you cannot profitably operate the sign(s), if you know what you are doing.