Hi,
Are you talking about Windows Explorer (file management app) or MS Internet Explorer(IE) the Browser? If it's IE, that's a very common symptom of virus/malware infection (you checked that using good tools it appears), or further Windows system file corruption. Sometimes even if hardware is ok, Windows just can't be repaired with software tools, and you may have to bite the bullet and perform a Windows reinstallation or Windows Reset as we call it in the biz.
Often, when 1 or 2 browsers go, Windows is seriously ill and needs to be refreshed or reset. You could download firefox or safari for windows and try those too-if they are also broken; most likely your Windows needs to be reinstalled.
If you have factory Recovery discs...