it sounds like you might be behind a router and have ports forwarded to your computer... but your computers LAN IP Address has changed, so you might need to go and change the IP Address that your ports are forwarded (use ipconfig /all to confirm if your LAN IP Address has changed) - this will normally only happen if your computer is turned off for a few days, however if the router was also rebooted at the same time as the computer (eg. by a brief power cut or something?) then it would happen instantly as the router would forget the IP Address it gave the computer the last time
