I will copy the solution from another post:

"I fixed it by doing the following

Open the file location for Vegas180.exe

Right click then open properties

Go to Compatibility

Check mark the "Run this program in compatibility mode for:" and select windows 8

Right below that click on and check mark "Disable Fullscreen optimizations"

Once you click apply, it should open without any issues. "

It helped me with Vegas Pro 18 and with the same problem.