You can try the free version of Malwarebytes. It is highly recommended on this Forum. After installing on your computer make sure you get the latest updates. Select Full Scan. Then select which drive(s) you want to scan. A full scan could take over an hour.
Tariq: Eset online scanner is also very well regarded. It is also free. I would run both Malwarebytes and Eset scanner, but not at the same time. run one, then the other.
These are both scanners, not real-time protection.
Consider free AV - Microsoft Security Essentials, or Avast, or AVG. You only need one, more than one AV program can cause issues as they tend to compete for resources and they might consider the other application a security risk. So only run one real-time AV program on your system.