And with that minecraft launcher, you should try that thing what it basically tells you. Go to the files C:\Users\NAME\AppData\Roaming\.minecraft\versions, then delete all files with 1.8 minecraft, so when you start the launcher again, the 1.8 will be fully installed again. If this won't help, save for yourself stuff from C:\Users\NAME\AppData\Roaming\.minecraft, very important: saves, textures, screenshots too
, so copy those somewhere else and then re-install the whole minecraft. Then it have to be working.
P.S.: you can get 1.8.9
If you'll need more help, feel free to ask.