Please be specific in your description!.... Describe exactly what happens when you click on the icon and if the splash screen comes up, what happen or which messages do you see?
Just a suggestion ... try going to the Task Manager and if there are any Vegas Pro items listed there, hit the End Process button on each entry until they are all gone. Then try opening Vegas Pro 18 again.
After your comment, I thought that turning off the computer might stop any Vegas Pro items that were running in the background. Gave it a try and it worked. Vegas is back on the line. Thank you!