The best way is to start your computer in safe mode hitting F8, then choosing Safe Mode with Networking. Google, download and install Malwarebytes, it will check for malware. Google & download Avast as well. Install them one at a time, you can download them both at once if you want then just remember where it was downloaded to. Run the malwarebytes first then install and run Avast. It will tell you whether or not you got a virus. If not run CCleaner (you will wanna run CCleaner after the malware & virus check anyway for registry errors) and Defraggler.