Avast Internet Premium refusing to start!

Hi there.

I installed Avast Internet Premium Trial.
Turned on my pc today and it Refuses to engage.
Turn it on, And it immediately Turns off!
Any Ideas!

did you uninstall your previous used AV according to vendors instruction before you installed avast ?

General: Uninstalling a third-party antivirus software http://www.avast.com/en-eu/faq.php?article=AVKB11#artTitle

Why Using Multiple Antivirus Programs is a Bad Idea http://blog.kaspersky.com/multiple-antivirus-programs-bad-idea/