Installing channel balances

Hello -

To the best of my knowledge I followed the instruction video on how to install non-tilting window sliders. Maybe I'm the only one who thinks so, but I get the feeling those instructions could use some work.

I ordered and received two channel guides, to replace the old ones, only one if which had actually broken, but I thought I might as well replace them both. The first one was a bear because I could not get the little hook into the little square hole until I slightly bent the hook and slightly scraped the hole with my screwdriver. Then I pushed the guide down (this takes some pressure; I'd recommend pushing it down with a block of wood). It seemed to be in place, held at the top by the pop-out hook. Next I installed the second one, but it popped out and after that the bottom hook inside it seemed to be misaligned. I put it back as well as I could, but then the string inside that guide broke, so it was useless.

At that point I decided I might as well install one of the old guides, the one that seemed to be undamaged, so I'd have a functioning window. That one installed just fine, but a lot of good all of this has done, because after I put the window back into the frame the guides don't hold it in place. They seem to be totally useless.

Hopefully one of your experts can tell what I'm missing here. I attach pictures of the guides in place.