Protect Your PC Against virus: Check A Website For Malware

Hi. Though I have an antivirus installed in my PC, it is not working properly from a few days because the PC has slowed down and I cannot even find out the reason why. Whenever I put the computer on full scan, it does not show any abnormalities either nor does it report a problem-related to the websites I visit. Can you please suggest me a way to check a website for malware? Thanks in advance.
