I signed up with the amazon affiliate program a while ago and started displaying their ads on my video games forum and my computers forum.
I have not earned a cent from it yet. Nothing has ever been bought on my sites.
I am thinking about taking the amazon products down and replacing them with adsense ads.
What do you guys think? Any tips to get people to buy amazon products on my sites?

I don't know, it's a hard thing to do. My friend used to have it on his forum with little results. I believe adsense is better.

What kind of books are being advertised on your site? Do you have books on video games on your games forum and computer books on your computer forum?

Yep, pretty much. It's not books however.
On my Video Games Forum, there are amazon ads of video games and game consoles and hardware. On my Movies Forum, there are ads of movies as you would guess it.
Amazon is not just about books.

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Then you should get visitors buy amazon's goods. People generally post on forum to gain knowledge and to share knowledge. Gaming forums help posters to learn the tricks of the game. So they may not looking for buying games.
I suggest you to put a sub forum containing posts related to recommendation of new games and new game press releases etc. Whoever visits that may find interest in amazon ads.

Of course at other sub-forums you need not use amazon's ads as they may not be fruitful. Use adsense on other subforums.

I tried amazon for one of my sites and didn't make a penny although I do have friends that have done very well with them so i guess this depends on how related your content is.