Delete Silence button not working at all...Help?

I'm assuming that this is a PC. Usually when Audition gets stuck it's because the Operating System has decided that what it wants to do is way more important than anything the user could possibly need to be getting on with. Anti-virus software scanning can cause it, as can WiFi signal searches. Or even something as simple as trying to access and resize the temp file space. And I expect that there are a lot of other things that can, too.

If you do a search, you'll find plenty of information around about optimising Windows for audio use. They generally say the same sorts of things, and it's generally worth working your way through them. It may not completely stop this happening, but it should at least reduce the instances. It's also well worth putting Audition's temp files in a location that isn't shared with the OS. Creating your own folder for them on the root drive of your system is generally the way to go.