Well. How attached are you to win8?
Seriously though... try uninstalling all LMMS files (you can keep your projects/presets etc.), then running a registry cleanup (or whatever the equivalent is for win8, I'm not sure if "registry" is still a thing, the last windows I used was xp), run an antivirus scan, and whatever problem-solving tools windows provides for you... Then try reinstalling again.
CCleaner is something that is often recommended for registry cleanup, again not sure if this applies to 8.
Not much else to say really. Hope you get it working.