When installing antivirus on win 7 64 bit wont boot

Hello,
I recently attempted to install Anti-virus software on my Mom's HP laptop running Win 7 Home Premium. After that, the system would not boot. So I did a System Restore, and tried again thinking the Defrag I did after messed up the files. I then tried to install it again. Same result. At that point, I figured I would part ways with what I was using, AVG free 2013, and try Microsoft Internet Security Essentials. That ALSO produced same result. The only thing I could think of was that she had some kind of software conflict vying for the same space in the machine. She has a Norton online back up program installed and CC Cleaner, neither of which seem to be an antivirus. Can anybody shed some light? Her OS is 64 bit.