Did you get it from:
http://code.google.com/p/sigil/downloads/list
This is the official download site. I too am running Windows 7, 64 bit and it installed and is running on this computer.
Sometimes antivirus programs can interfere with installation. You can try turning off the antivirus program temporarily while you install Sigil.
If these ideas do not work, please tell us what message you are getting when you try to start Sigil.