When this kind of stuff happens it's important to be entirely sure, you need to completely reformat your computer
Back up your needed files;
1. External or extra hard drive connected
2. Google drive
3. Dropbox
Reformat your computer.
When reinstalling windows, select the drive that had windows on it and select 'reformat'. Will take a second and the hard drive will be wiped clean.
Select new installation, install.
Hook up the external HD and drag your files back over.
Seems a bit extreme, kind of like rebuilding your motor, because your water pump is bad. Lot's of ways to fix a browser hijack without a complete wipe...