It seems like i can't grab things anymore. When i try, i pick up things with my hand but can't keep them. Is their something i can do ?

There are some items you can't pick up. Also don't forget if you need to drag an item to/out/around your inventory you need to click on it and hold the mouse button down.

It's a book i can't grab. And also i can't search some dead body i've just killed. I'm in the Quests of Wintherhold and try to Focus the Oculory. Can't grab the books.

I think you've got the wrong forum there buddy.