This is the online installer that is failing. I'll need the installation log file to investigate further. Please provide the Adobe_ADM.log file saved at C:\Users\<YourUserID>\AppData\Local\Temp\Adobe_ADMLogs using the instructions The specified item was not found. to upload the file to cloud.acrobat.com or a file sharing service of your choice and post the URL in your reply.
The offline/standalone installer should work and is posted at the bottom of the Installation problems | Flash Player | Windows page in the 'Still having problems' section. Please do provide the Adobe_ADM.log file as it will help us understand why the online installer is failing.