Internet icon has yellow exclamation mark?

Yesterday, because of outside works in the neighbourhood, we had a power cut all day. Naturally, the router and the Internet was off. Now it's back on and my computer has this yellow exclamation mark. Internet is fine on my phone and my mother's iPad, but my pc uses a cable and there isn't any Internet access. Troubleshooting can't figure it out. I've tried turning the router off and on again without luck. I tried system restore without luck. I'm 18 and definitely not savvy with technology so I don't know what to do. I have a deadline tomorrow for an assignment, so I really need to fix it so I can get on my university intranet.

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