OK i have a d620 that I replaced the motherboard on. I bought it from a website and i have a bios password that will not...

Your cable may be lose on the motherboard. Check Lenovo's website to see if they have an instruction for removing the keyboard and reinstalling it. If that doesn't work you may need to get a replacement keyboard.

Mine was doing the same thing and it turned out that the onboard video chip was going bad. I located a "remanufactured" motherboard on line and replaced it. Works fine now.