Sometimes I have the same problem. I am a biologist. People happen to ask me all sort of things about health (but I've never worked on humans) or their plants (but I'm a zoologist). Lots of times I have no clue about the death of their geranium. So I came up with this solution: when people ask me what I do for a living, I tell them that I study a specific aspect of clams. I never mention being a biologist, even if it's implicit. This sends the message that biology is a huge field. They won't refrain from asking me about that weird behaviour of their goldfish, but they won't expect a full answer.
At the beginning of our interaction, my friends (and the people that ask you for technical support) place themselves at the stage of "unconscious incompetence" in the four stages of knowledge.
The individual does not understand or know how to do something and does not necessarily recognize the deficit. [...] The individual must recognize their own incompetence, and the value of the new skill, before moving on to the next stage.
They just do not know that being an expert in computers is not a thing. They probably equate it to being expert in washing machines or toasters or whatever appliance. To get out of this incomprehension and step to the following stage, which is "conscious incompetence", they have to realize what you do for a living. So bargain some explanatory time before starting helping them:
Alright, I'll try and help you. First of all, however, I need you to listen to me for two minutes, okay?
Then you can explain to them in simple words which "computer part" your work is about, using comparisons you know they will understand. You can choose to make it a bit lengthier, to get them the feeling of the complexity of the subject, but don't be condescending, as it would backfire:
So, this is your PC. It is composed of the "body", which is the hardware, and the "soul", which is the software. I work with softwares. Some people deal with the body, some with the soul. You wouldn't go to a dermatologist to get psychotherapy, right?
(Well, this is just a crummy example, I'm sure you will come up with a better one...)
Now state that you're not the one they're looking for, but that you'll be glad to help to the extent you can:
In your case, you would need a "dermatologist", while I'm a "psychologist". What I can do is look for a solution with you. Did you try googling {X}?
This approach takes time, but if the people asking for help are always the same, it could be worth it. A shorter version of it is referring directly to their work for comparison ("I can't help much. Could you help me if I asked you for {Y - somehow related to their work but not really}?").