The BIOS may not support it and the new CPU may make power demands the motherboard can't supply. To fix this may require the laptop maker's support.
I have an ashton digital maximate 500 notebook with a PIII 650.socket 370 I upgraded it with a PIII 1.0GHz socket 370 it fits, but will not bootup. i took out the battery to clear the CMOS, but no joy. anyone has some advice on how to boot it up.