MacBook Pro Mid-2012 video output?

So, I've had my laptop for 5 years.

I've been to the Apple Store 3 times, and my computer is now out-of-warranty.

In 2013, I had a liquid spill issue with my computer. I didn't use it, for 4 years, until I discovered I needed an additional computer.

I had my neighbor change the RAM, because the computer turned on, but couldn't get past the Apple logo screen. He then lost my RAM, so I had to buy new RAM myself. My neighbor helped me put the new RAM in, and then I discovered that I would turn the computer on, and there was no video output.

I called Apple Support, and I was told that I either need a Mini DP to HDMI connector (which I have now, but didn't at the time). I also tried key tricks, like Command/Option/P/R (which didn't work), and others that didn't work.

Was this reliable advice, because I have no video output on my Macbook?

And I have also tried the "quilt test", which didn't work on the computer either.

Can anyone help me?