An unpleasant thought, but there have been instances of "tech support" places that "harvest" hardware (graphics cards, sound cards, memory, hard drives) out of customer's machines. Sometimes with the excuse that "they were broken".
I've done that myself, in a sense, when I discovered that a friend had put a graphics card in their machine, when in fact the on-board graphics were better than the card! I needed a graphics card for another machine, so I "stole" it. Actually, this was done with that friend's full knowledge and permission.
So... is their a chance that you had a graphics card before your machine went to tech support, and you haven't got it now?
(They might have genuinely made a mistake - removing non-essential hardware to track down a problem is standard practice. They could have taken out a graphics card, sorted out the prior problem, then forgotten to replace the card.)
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"Striking up conversations with strangers is an autistic person's version of extreme sports."
Kamran Nazeer