Cold Fusion ate my webserver!
The only means that I know of that Cold Fusion can lock up IIS is if IIS is only configured to allow a certain number of tasks to be executed. For example, Personal Web Server will only allow two tasks to execute at any given time.
The snag here is when you perform a call against the database. If a third-party call (such as a database query) does not respond back to Cold Fusion, CF will sit there and wait forever until the database sends something back to it. Timeouts do not apply here.
If Cold Fusion never finishes a task and therefore never notifies IIS that it has finished, IIS will keep waiting for it and you'll eventually run out of free "sessions" and IIS will stop responding to new page requests
Under Windows 95/98, the only option is to reboot. Under NT, you may be able to stop the Cold Fusion service to see if it'll free up the tasks. Otherwise, you'll have to reboot.
But you need to look into your database access to find out where the problem lies. It's not with Cold Fusion, it's with your database.