|First download and burn an Antivirus LiveCD, which boots it's own operating system so that windows is not running, and scans your system for viruses.|
When finished, reboot your computer in normal mode, download and install fresh antivirus software, even if there is already one installed to your computer.
When installed, update the antivirus definition files.
Download and install Malwarebytes and let it run.
While it's scanning your system, the newly installed antivirus software also scans all files for infection.
After that, download and install Ccleaner and let it run.
When finished, reboot your computer and check if it's working as expected.