I recommend downloading
MalwareBytes Anti Malware free edition, selecting the Settings tab across the top of the Window, selecting the Detection and Protection tab down the left of the Settings section, selecting Scan for Rootkits and setting PUP and PUM to Warn User About Detections.
Now that that's set, navigate back to the Dashboard tab across the top, select Update to the right of the Database Version section to be sure you have the latest malware definitions, wait for that to complete then navigate to the Scan tab across the top, select Threat Scan if it's not already highlighted and click Start Scan. It may take up to an hour to scan depending on the size and speed of your hard drive(s).