The Newgrounds Player currently doesn't seem to work because of Windows blocking flash. There are solutions and workarounds for this, I'm going to link you a solution by Sonucais:
https://sonucais.newgrounds.com/news/post/1137244
Tom said that they are looking for ways to include that solution in the install process, so alternatively you can wait for the Newgrounds Player to be updated but I don't know how long it will take for it to get an update.
Another solution that I've heard of is to change your computer's time and date to before the end of flash (like set the year to 2020) to get the Newgrounds Player to work again.
DragonFang324
I'm not mad about it and I don't mean to complain, but I really want to play and?or watch these Flashes again really badly.