avast won't open?

Hi. I have had avast internet security for some time without any problems. I wanted to run a scan today however it won’t open? Could this be a virus? Does anyone have any ideas on a fix? Cheers

Please provide more details.
Keep in mind that we can not see what is happening on your system, meaning you will have to inform us.
What OS/SP?
What exact version of avast?
Any other security software installed/running? (or did you have before)
Any error? (If so what exact error)