If you are unbale to find the w3wp.exe process that we attach our VS debugger to inorder to step through X++ on D365. Chances are the windows logging service is not running. The service name to check is W3C Logging Service start this service by going to services.msc and reopen/refresh the process list.
P.s Also make sure your World Wide Web Publishing service is running. Without which your D365 client wont be hosted as well.
For more details on how to debug D365 have a look at the MS blog: Quick and easy debugging in AX 7