Shutdown your Mac.
Restart and, as soon as you hear the startup chime, press and hold the “OPTION” key at boot until the boot menu appears. (Alternative: Restart, hold COMMAND + R keys until you see the Apple logo and progress indicator. If neither of those work, try COMMAND + R + OPT.)
Then, select the “Recovery" volume.
Wait for “OS X Utilities” menu to appear (DO NOT RE-INSTALL)
Click on the “Utilities” option in the menubar the the top of the screen and select “Terminal”
Type the following at the prompt:
and press Return on the keyboard.
Select the Macintosh HD volume and the user account. To change the password, type it in both places, and a hint, then click the Save button.
Restart your Mac and, hopefully, you can now use the pasword to install Silverlight.If you still have concerns, please do not negatively rate my answer, simply reply back before rating. I'll be more than happy to work with you further
. Hopefully, this info will answer your question. When you are satisfied, please give my answers a positive rating. You are judging my personal service only (not this website, the price, or your issue) and high ratings assure I remain in good standing.
Thanks, happy holidays, and good luck,