Hello, I have wrote a batch file to fix your Minecraft installation.
Just copy the following script and save it as a batch file in any text editor.
echo Minecraft Fixer Script v1
echo This is a script to fix common problems
echo with Minecraft.
echo Post in the original Minecraft Forum thread
echo if you encounter any problems with it.
echo Now, please stop Minecraft.
echo Please backup your saves directory before you proceed!
echo An Explorer window will be open.
Get the Minecraft working directory
set /p mcdir=Minecraft working directory (press Enter for automatic detection):
if "%mcdir%"=="" set mcdir="%userprofile%\AppData\Roaming\.minecraft"
if not exist %mcdir% echo %mcdir% was not found&&goto :enter_directory
echo Deleting assets directory...
del /f /s /q assets
echo Deleting libraries directory...
del /f /s /q libraries
echo Do you want to delete the versions directory?
echo If you're using mods / Forge, you'll have to reinstall them
echo For the first time, it's recommended to answer 'no'.
echo If this does not work, restart the script and answer 'yes'.
set /p deleteVersions=Delete versions directory (yes/no)
if "%deleteVersions%"=="yes" del /f /s /q versions
echo Now you're done! Press Enter to close this window and restart minecraft
NOTE: I have Linux and wrote this based on my command knowledge. If this does not work, please say so!