For Office 2007 retail products like Home and Student, uninstalling from old PCs does not automatically “free” activations on Microsoft’s side. When the activation limit is reached and the original machines are no longer available, the supported path is to use phone activation and speak to an agent who can reset/allow activation.
Use the telephone activation route even if the exact error text does not match what is shown in the article. During the call, stay on the line through the automated prompts until connected to a real person, then explain that the old machines are gone and that the license is only being used on the current PC. The agent can typically help complete activation without needing to remove anything from the old computers.
The phone number to call depends on the region and is listed in the article referenced below.
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