It doesn't sound like writer's block. It sounds like guilt.
You have a book, and you want to finish it, but you have all these new, fresh ideas, and the creative drive to bring those new thoughts into fruition, but can't because you subconsciously feel guilty about ditching the old book to write that "something new".
Your mind is hesitant to continue because you keep looking back.
Ask yourself, Do you honestly believe you'll come back to the old book later? or is it truly a lost cause?
You knowing the disappointment of picking up, and reading, unfinished books rings off in your head.
I think every Author knows this kind of disappointment. -And because of it, there are those that will tell you to finish it, or take a break then finish it. Do this, or do that, then finish. It needs to be finished. Readers would want it to be finished. You already published, so it needs an end. It's expected to have an end.. etc etc.
But you just have to tell yourself, "An unfinished book is fine to leave behind"; Working on something else is okay. Maybe, one day, you'll feel motivated to look into, or rewrite, or continue the old book. But you have to be honest with yourself today. Maybe it just isn't that time. It could be for a multitude of reasons: The genre is taxing on your psyche. You don't feel adequate enough to give the emotion the book needs to portray. It's too serious of a novel that doesn't mix with your own personality; Maybe it isn't serious enough. There's tons of reason why your mind isn't mixing with this book.
Let it sit. Give it a week. Read it from the start until the part you wrote up to. Either, you like what you're reading, and will look forward to continue writing, ...or you just don't, and It's just not your style. Whichever you choose, it's fine. It'll be fine, the world goes on. Put it aside. You don't need to forget it exists, but know that it needs to be pushed aside. Not because you hate it, but because you need a break from it. You can't work yourself over for not giving it the attention its begging from you every time you want to write the other stuff. Make an archive. A personal shelf, or file where books can sit, and wait.
If you pick them back up, great! Enjoy writing.
If not, learn something about yourself from them. Why are they in the archive? What gave you the feeling: "this book is keeping me from writing"? Learn from it. Learning who you are as a person is always something worth looking into. Any little bit opens new doors.
I personally have an archive of.. (Let me check.) 28 either completed, unfinished, half-written, or barely started books that aren't published. Here on SH, I have 1 single book I'm currently writing, and it's my least serious.. My more serious books are longer, or more difficult to write. I use this book I have here to throw my random ideas into. It's a hodgepodge of nonsense. But it's a book.
Having other sources to dump your ideas can help clear your head for what you feel you need to work on, or even excite you to branch out into other genres. But the fact is, you need to accept that kind of attitude. You need to accept that some books, whether you love them or not, are sometimes.. unwritable.. -For now, at least. Maybe in the future, you'll have the inspiration to pick it back up.
Anyway, I'm no teacher, or psychiatrist. The only person that can figure out your head, is you.
-and medical professionals, but I'm trying to be profound.
