1. Motherboard. Did you buy the replacement motherboard from Dell? If so, did they say anything about a Dell indentification "tattoo" on the motherboard (BIOS)?
2. Installation Media. Did the laptop come with an OEM Recovery Partition (on the hard drive), OEM Recovery CD, or an OEM Windows XP setup CD?
Are you attempting to reinstall an OEM licensed version of Windows XP?
3. OEM Windows XP License. I'm reading reinstallation of OEM Windows XP media onto a computer with a motherboard replacement (Dell or third party) is problematic because the major brand computer vendors are expected to build in safe guards to restrict the license to the original computer.
Dell 2350 motherboard replacementQuestion about Dells BIOS locked OS4. Dell Support. Maybe you should call Dell to confirm or deny this issue. And if it is an issue what support (tools or options) they can provide to get beyond it.
Motherboard Replacements and Windows OEM EULAs