it is a networking issue first, unplug your networking after you check it first go cmd and type it ping 192.168.1.1 if ping reply then everything is good if ping show error then its networking issue make sure check your networking devices first
window defender is secure from malware and spyware virus but it is not protected from trojan horse virus I recommend using avg internet security antivirus it is not heavy as compared to Kaspersky antivirus