I'm not familiar with that particular model, but did have an older Singer machine. My initial reaction was that the 'pinkish' tension spring is broken. It should be a continuous loop with both ends fixed into the disc housing. It can then move up and down to even out the tension on the thread. You thread the discs by passing the thread through the tension discs, over the loop, then through the 'blue-ish' guide. On my machine, you did not pass the thread through the (pink) loop.
As I said, I don't know the particular model.
Here's a link to a site where you can buy a manual. Sorry I couldn't find a free download, but there might be one out there.