open an admin command prompt, type
ipconfig /flushdns
if that doesn't work, try clearing the arp cache:
netsh interface ip delete arpcache
next, if required, reset winsock to defaults with these 3 commands, pressing enter after each one. Reboot required.
netsh winsock reset catalog
netsh int ipv4 reset reset.log
netsh int ipv6 reset reset.log
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