1) What is new or different since the last time everything worked properly (ie, new hw, new sw, virus, error, etc)?
2) Is Windows Update allowed to install drivers? Have you recently updated or installed any drivers?
3) Look in Device Manager. Are there any yellow or red symbols?
4) What version of Windows are you using?
5) What type & model computer are you using?
6) Please run full system scans with BOTH your installed anti virus app and with MalwareBytes