No major changes in the world until 1975. But then.... without Gates, no Microsoft, and Paul Allen either never writes Altair BASIC or does it without Gates as his sales/strategic-vision guy.
Even before MS-DOS, Microsoft provided programming software for many computers, including Apple ("Applesoft BASIC" was made by Microsoft), and Radio Shack ("Color BASIC" for TRS-80 Color Computers) as well as the Softcard (allowed Apple II users to use the CP/M operating system, MS-DOS's ancestor and cousin) and XENIX (Microsoft's first OS - a UNIX-based system first released in 1980).
This doesn't mean every last bit of the computer industry is changed at first; Apple IIs initially used Wozniak's Integer BASIC, and Commodores used their own BASIC as well. However, even before IBM steps in, there are going to be significant differences from OTL...
Assuming there is even still an IBM PC, and one similar to OTL, the chief Operating System is going to be either CP/M-86 (port of CP/M) or the UCSD p-System (OS based on the Pascal programming language also used on IBM DisplayWriters). The PC won't be using Microsoft BASIC (in either ROM BASIC, BASICA, or GW-BASIC form) either, but something else, either home-grown or from another company.
From that point onwards, its hard to predict. An easier POD would have been "WI Bill Gates never buys Seattle Computer's QDOS" or "WI Bill Gates killed in a car accident in 1979"... because Microsoft, believe it or not, was a fairly important player in the early computer field - albeit one in a particular area (programming tools, mostly BASIC interpreters). With a different BASIC instead of Allen's, or no BASIC, Altairs might not sell quite as well, or be sold to different people... there might not even BE an Apple Computer (founded almost a year after Microsoft), let alone a Macintosh.