Fuses have a tiny piece of metal inside of them that is designed to fail whenever too much power goes through it. This will stop power from continuing through the circuit.
Although it may seem like you can tell whether or not a glass fuse is broken by looking into it, this is not always the case.
If you have a fuse that you believe is blow, then the best thing to do is replace it, even if it appears to be fine. If this doesn’t restore power, then you will need to call an experienced electrician to troubleshoot the problem for you.