Git .gitignore not working

Git .gitignore not working

I am having some problems with my GIT repo ... I have a few folders added
in my ".gitignore" file. They contain over 100k files. Mainly images, tmp
and cache stuff. What I need is to be able to commit changes to my code
with out commiting what happens in those folders. I thought adding them
into the ".gitignore" would do the trick but for some reason it's not
working at all... I havant been abble to commit anything to the repo in
days because every time I try the push command it trys sending 100k files
then it frozes and times out.
root@serveur [/home/***/***]# git push origin master
Password:
Counting objects: 110300, done.
How can I force GIT to reindex the tree while taking in consideration the
ignored folders so I can finaly commit all the changes I made to the code.
A merge is planed today !