Can't get it to start up, can't re-download either

I can’t get Avast to start up. Does nothing when I click on it. Yes, I’ve tried re-downloading it too. It gets to like a bar of completing then just vanishes. What do I do? Thank you, guys!

What was installed prior to Avast? How was it removed?
Check my signature for Successfully installing avast if you had something else installed.
If you only had Avast installed, follow the link for repair and clean install.