I think you may have worms as they can turn your plants to goo. can you take a picture? BT might fix your issue if that is the case.

Sounds very much like Squash Vine Borer. The larva are inside the plant and eat the stem from the inside out.

I had that problem last year and have managed to keep the borers at bay this year with a combination of homemade insect soap on the stems once a week, Neem soil drench, and supervision. Unfortunately the bugger did not produce as well as I would like (I think too much nitrogen as it is lush, green and succulent) and I have a new one started.

I planted a trap crop of Hubbard...lost one and one got infected but survived. But when I saw they were thriving started doing the same for them and now have Hubbards growing. I also have quit seeing the borers flying around (I was seeing them every day so I know they were doing the nasty on my stems)

Next year I am going to try a trombicini and see if it is a good zuke substitute.

Of course, now the yellow squash is battling pickleworms. Should have planted earlier. That is another topic though.