Hi,
Depending on what sort of password it prompts will determine how to try to fix this.
If its a Sleep system password (ie you laptop is in hibernate mode and you are asked to type in a non windows password), you need to take the battery out of the laptop and try and reboot it that way (you might need to leave it out for 30-60 mins).
If this doesn't work, then you can try taking the laptop to bits, finding the CMOS Battery on the motherboard and then taking that out... (be careful though, because this will void you're warranty - i would only do this as an absolute last resort!)
If you can now get to the first boot screen of the computer you should try resetting the password, so you dont get into future bother with it. To do this, i recommend using one of the tools on Ultimate Boot CD : http://www.ultimatebootcd.com/
Use burn the image to CD and boot from CD. Its quite self explanatory.
Direct img link : http://ubcd.mirror.fusa.be/ubcd503.iso
If its a windows 7 password, then look at this link and use this tool to reset it :
Win7/2k/XP/Vista Password recovery : http://pogostick.net/~pnh/ntpasswd/
Let me know how you get on...