A: Speaking from experience, it's doubtful that MSE or any other anti-virus/antispyware application would install (or install properly) on an already-infected computer.
You have two choices:
1. Back up your personal data (none of which should be considered 100% trustworthy) then format your HDD and do a clean install of Windows.
NB: A Repair Install or In-Place Upgrade will not fix an infected computer!
2. See if you can get the computer cleaned-up with the assistance of an knowledgable expert in such matters. You will find such assistance in http://spywarehammer.com/simplemachinesforum/index.php?board=10.0,
http://www.bluetack.co.uk/forums/index.php, and other appropriate forums.
MS PCSafety also provides home users (only) no-charge support in dealing with malware infections such as viruses, spyware (including unwanted software), and adware. Start here: https://support.microsoft.com/oas/default.aspx?&prid=7552&st=1
Protect Your PC
5 steps to help protect your new computer before you go online
Steps To Help Prevent Spyware
Steps to Help Prevent Computer Worms
Avoid Rogue Security Software!
~Robear Dyer (PA Bear)
MS MVP (IE, Mail, Security, Windows & Update Services) since 2002
Disclaimer: I neither represent nor work for Microsoft