Is the TV show Ancient Aliens in any way credible?
These are two separate questions.
Question #1 - Is the television series, Ancient Aliens credible? - The answer is almost certainly no. No compelling evidence from a credible source (or sources) has ever been presented that alien lifeforms ever visited the Earth, much less interacted and influenced any ancient cultures.
Question # 2 - Could ancient civilizations move huge stones without the modern machinery that exists today? The answer is yes.
- Had large numbers of workers who could be tasked to work upon projects of all sorts. These were both freed people, skilled craftsmen and on occasion, slaves.
- Had draft animals which they could use to assist in hauling items over short or relatively longer distances. It has been shown that few major monuments were built with stone that came from farther than 20-50 miles away. If the stone came from farther away, it was rarely the heavier foundation pieces but mostly decorative ones.
- Possessed knowledge of the first tools of man including: The wedge, the lever and fulcrum, the screw,the wheel and axle (except is Mesoamerica where it was only used on children's toys), the pulley and the inclined plane. These are all machines which are used in construction today
- Used many of the same engineering techniques which are used today.
- Were working on structures which held significant religious as well as social meaning to them.
There is no reason to believe that they weren't able to find the methods necessary to erect massive structures. And their "mistakes" can be seen in constructions such as the Bent Pyramid in what is now Southern Egypt.
That they someone need "alien influence" is both ridiculous and somewhat racist. Unfortunately, programs like Ancient Aliens propagate those fallacies.