Narrow down the failure
Record the affected address and message without publishing personal content or credentials. Try two other familiar websites. If only one page fails, visit the service's homepage through an address you enter yourself. An old bookmark may simply lead to a removed page.
Then compare another browser or a private window. This is a diagnostic step, not an instruction to move confidential work into an unapproved application. If the site works there, extensions, stored data or the browser profile may be involved. Avoid immediately clearing all browser data, which would also change unrelated sessions and settings.
Notice the type of message: not found may refer to a missing page, while a timeout means a connection was not answered in time. An explicit access denial may concern authentication or permission. Record the wording before closing the window. Remembering only a general failure makes it difficult to tell whether a later test changed the behaviour.
Compare device and network separately
Try the same public page on a second device using the same network. If it fails everywhere, check the service's official status information. Where permitted, comparison through a mobile hotspot can indicate whether the original connection is involved. Account for data allowances and work-device policies.
DNS translates names into network addresses. A DNS-related fault can therefore prevent an otherwise reachable website from being found. That does not mean choosing an arbitrary new DNS provider is the right solution. In a work network, name resolution, filtering and VPN access may be deliberately coordinated. Do not change that arrangement without responsibility for it.
Do not bypass security warnings
For certificate warnings, first check the computer's clock and the exact domain. Do not simply accept an unsafe exception and enter credentials. An incorrect clock is one possible cause, but a mistyped address or server problem also needs consideration.
A support report often needs only the domain, time, error message, browser and comparison results. Include whether a VPN was active. Leave out passwords and complete confidential URLs containing access tokens. This evidence enables a focused investigation instead of resetting the entire router without a clear reason or changing several unrelated settings together.
