Just like andrewsi (see comment below the original question), my instant reaction to the question is Captain Power and the Soldiers of the Future, a partly live-action / partly CGI-animated, post-apocalyptic 1987-1988 Canadian television series that also aired in the US.
The relevant plot points are:
- Intelligent machines ("Bio-Mechs") created by Lord Dread have taken over the world in the 22nd Century and are hunting down and subjugating the remains of the human race (survivors are "digitized" and stored in a supercomputer called "OverMind")
- Captain Power and his team of soldiers lead the resistance against Lord Dread's machine empire
- They mainly carry small arms
- The show has a gritty, dystopian feel with muted, dim hues
Finally, you can see the pyramid-like fortress of Lord Dread at 00:30 in the show's intro sequence:
Interesting Side Notes: J. Michael Straczynski (of Babylon 5 fame) was a writer for the series, and the show featured semi-interactive elements that responded to toys released in conjunction with the show. Also, costumes from Captain Power were recycled and used for the Borg on TNG....