My Kindle4PC stopped working too. It's annoying that there was no indication what the problem was. I remember reading here that Amazon posted on their forum that the warning about it expiring was a mistake and it wasn't really going to happen.
I normally open the program to upgrade. I guess I have to completely uninstall it and reinstall which is kind of annoying. I hope there are some real improvements to make it worth the trouble.
I guess I will have to also have to find updated tools also. I rarely ever use them on my Kindle books because most of the books I bought were freebies and I have so many, it would take a lot of time and space to convert them... but I like to have the tools available just in case.
Speaking of books... I bought a few free books on Amazon today and when I click to see the purchase receipt, they are all listed on one page as "pending". I've never seen this before. I also did not receive the purchase confirmation emails like I normally do.
Has this happened to anyone else? Could it be because I chose "send to PC" and have not updated the software? It's very strange.