Como arreglo lo que le pasa a mi laptop

Hola,

Mi computadora era Windows vista y la cambie a Windows XP y ahora me dice esto cuando la prendo, This copy of Windows did not pass genuine Windows validation and you have not yet resolved the problem. This copy of Windows is no longer eligible to receive the full range of upgrades and product support available from Microsoft. To protect your copy of Windows, click Resolve Now. This copy of Windows must be activated with Microsoft before you can log on. Do you want to activate Windows now? Que debo hacer.