System restore

Hello,
I have windows vista and my system restore does not work like it used to. Suddenly the icon turned blank or white. I figured out that i needed to turn on system restore by checking the hard discs in 'system properties', but it still doesn't work. I tried to resolve the problem through the internet; found the box that tells me to check a restoration date which i did. Just, after the process when my computer turns on again, a message appeared saying that system restore has not completed succesfully, and that nothing has changed. I tried it a few times. What could be the problem and how do i fix this?

thx!