My 12-year-old grandson does not have any interests other than video games. He can be a good student, but he does not turn in work and always complains about not having friends and nobody liking him. He does not want to participate in any activity and when he does it is not for long. He often comes up with "get rich quick" ideas and has an answer for everything. He does not seem to be affected by any type of punishment. Any help would be appreciated.
Your grandson sounds to be intelligent albeit lacking focus or interest. Since he likes video games, you could try exposing him to programming where he could build his own games and share them with his peers. You're trying to find him a hobby that he enjoys and he could find friends wile doing it too. Exposure to a lot of different fields and activities is great for his age.
I do like jcmack's answer for it's positive attitude, but I'd like to point out that there is a huge gap between liking video games and making your own.
Games != Programming.
Programming is hard. It requires an incredible amount of attention to detail, a methodical mindset and the ability to accept to be told constantly that you're not as good as you think you are, because computers aren't very forgiving of mistakes - your program will just not work, or work in mysterious ways, if you make the tiniest of errors.
This doesn't sound like a very good match for your grandson (easy get-rich-quick schemes, has an answer for everything, doesn't participate in any activity for very long, ...)
(Also, it's a lonely hobby - you spend hours and hours alone, thinking about things you can't explain to anyone around you.)
I do agree with jcmack's thesis that since video games are the only thing your grandson seems to take an interest in, they will probably play a big part in approaching your grandson.
Figuring out which games your grandson plays, and why, might give you some insights.
For example, if he plays games against the computer, with no other human players involved, these games are often designed to keep you engaged. Some do this by allowing you to succeed repeatedly in quests/goals which are just hard enough that success is fairly certain, and then reward you with virtual loot, levels, points etc which might be recorded on a global scoreboard. Persistence in such games will steadily move the player upwards.
So if that's the case, video games might give your grandson a feeling of succeeding in something when success isn't common in the rest of his life, and that might be what draws him to the games.
OTOH, your grandson might not play against an AI, but against (or with) human players. For example, there are several games where teams of about 5 players band together to fulfill missions or quests (mostly revolving around warfare, either in realistic or fantasy settings). In such a game, your grandson might be a valued team member; he might have a status to defend, a role to play and social obligations to fulfill which all require that he play. If he's having trouble making friends IRL, he might get his need for friendship and status fulfilled from his online teammates.
So, in short: I think the video games fulfill a need that isn't met in the rest of your grandson's life.
My suggestion would therefore be to ask your grandson if he can show you what he's playing, and see if you can figure out why it's important to him. This won't change anything about the current situation, but you might get more insights into why he isn't interested in anything besides the video games, why he doesn't think anybody likes him etc. Sometimes it's hard for us to refrain from judgement ("you're wasting all this time playing this stupid game while real life passes you by..." when dealing with video games, but try to keep an open mind about what he shows and tells you.
This might provide you with enough hints to find things besides video games that would also help fulfill your grandson's needs.
How about some board games or tabletop games?
You could start with a family game night for Monopoly. Or you could learn about and break out some tabletop RPG.
This is a lot of work and a lot of effort, and the grandson likely won't appreciate it at first. But it has a lot of the same reward mechanisms as a video game while also being social.
Eventually you guys could even work together to develop a new board game or homebrew RPG. This can be really fun.
One day maybe you could even invite some of his classmates for a game night as well. Get some pizza, make it fun. Give him a chance to bond with them over something he already likes.