@luizman not starting would not be an issue with the CMOS (RTC) Battery. You do want to check your power supply dfirst. Make sure that you have the right voltage etc. then check the DC in jack on your computer and make sure that it is in good working order and not bend or corroded etc. After that download the service manual [https://downloads.dell.com/manuals/all-products/esuprt_laptop/esuprt_latitude_laptop/latitude-d630_service%20manual_en-us.pdf|from here] and disassembly your computer check the power in circuitry. Start with the easy things first; your power supply.