required the "Play Disc" to be present in the CD-ROM drive to launch. This changed officially in 2008 with Patch 1.12
: Manually copy specific files from your game discs into your Diablo II installation folder: From Diablo II Play Disc D2Music.mpq From Lord of Destruction Disc D2xMusic.mpq
. This allows you to download a digital version of the game that is pre-patched to 1.14 and specifically designed to run without a CD. Manual Disc File Migration
The most reliable way to play without a CD is to register your original CD keys on your account and download the modern installers.