How do I tell if it's my internet provider or my equipment?

Two checks settle it almost every time.

The modem lights. Every modem or fiber box has an indicator for the connection to the provider, usually labeled something like online, internet, or WAN. If that light is off, red, or blinking rather than steady, the problem is upstream of you and nothing in your office will fix it.

The direct test. Plug one laptop straight into the modem with a cable, bypassing your firewall and switch entirely. If the internet works, your circuit is fine and something inside your network is at fault. If it still does not work, it is the provider. Put things back the way they were afterward, and do not leave a machine connected directly for longer than the test.

Worth knowing: providers will often insist the problem is your equipment, because from their end they can see the modem and it looks healthy. A circuit can be up but degraded, losing packets in a way that makes everything feel broken while every light stays green. Proving that takes specific testing, and it is one of the more useful things we do on your behalf.