Laptop won't pick up the signal?

Hi there, my mum was a professional singer who died recently, for sentimental reasons I decided to convert a bunch of old cassettes on which she was singing to digitise them and then clean the sound up for family and friends etc.

So I started this job in May and got half of them done using a cassette deck and my laptop which was then running Windows 7.
I just recently returned to finish the job. The same laptop now has Windows 10 installed over the top of the old Windows 7, and as you can probably guess, I can’t get it to work. I’ve also tried a different brand-new laptop that I have, which also has Windows 10 on it, …no joy there either.

Audacity seems to be able to pick up my voice from my laptop’s on-board microphone, but when I try to play the tapes through a cassette recorder connected via RCA cables and the headphone jack into the computer, it still just picks up the microphone. I mean, Audacity is recording the tape, but only because it can hear the tape being played in the room, the signal is not going through the wire into the laptop as I would wish it. I have now thrown good hours after bad on this situation, and it’s driving me up the wall. There must be some setting or something I’m not doing correctly, though what I have no idea. Part of me is thinking, …… Is it something to do with the fact I’m now using Windows 10?

Just for your information, I have sent some additional photos to show the equipment I’m using, and how it is all plugged together. I absolutely don’t know what’s going on, please help regards, Gin
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I have corrected one photo and added two more
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Most laptops don’t the proper line-level inputs. The microphone input is about 100 times too sensitive for a line-level signal It can " but, it’s usually low-quality and it’s usually mono. If your computer has a single combo mic+headphone jack, the yellow RCA plug might connect to the microphone.)

The best solution is a USB audio interface with line inputs. The Berhinger USC202 is popular and inexpensive. it’s biggest weakness is that it doesn’t have recording level control. (I don’t own one.) Or, there a lots of higher-end audio interfaces. Do not buy a regular “USB soundcard” because they are like laptops with only mic-in and headphone-out.