You might be able to prevent the widespread adoption of the Internet if the old traditional AT&T monopoly on telephone wires and anything attached to them was maintained. That wouldn't prevent high-speed communications between large businesses and universities with the ability to run their own wires, but it could keep the Internet out of homes for a while. Of course cable companies would have to somehow be prevented from installing alternate wiring for their own purposes or things would just bypass the phone systems.
Here's a possibility: Instead of coming out with a PC, IBM does the same thing DEC did. They come out with crippled, low-end versions of each of the several IBM lines that came close to being a PC, with proprietary operating systems and a mainly closed architecture. The personal computer industry keeps bumping along with mainly incompatible 8-bit computers for another several years, with IBM loyalists in the IT departments of most companies sticking with IBM products. AT&T was broken up partly so they could compete with IBM in the computer market. That doesn't happen because the computer market doesn't grow anywhere near as fast without a standard to rally around, and there is no dominant force in the computer market. AT&T resists use of their lines for non-AT&T products, delaying mass-production of modems.
And that still doesn't get to where the OP wanted to be. You could delay the personal computer revolution by several years, and the mass advent of the Internet by a similar amount of time, but eventually processors and memory and all of the other elements would emerge, and you would end up with something similar. Computers might be based on Motorola 68000-series chips instead of Intel 8X086 chips, or it might have even been based on one of the more exotic alternatives like the Zilog Z8000, or the high-end 6502 successor Commodore was working on (the 65000), but the pieces would have eventually come together.