You don't say what OS is on the laptop or its make. Have you tried 'Safe Mode with Networking' link text to see if you can gain access that way?
As another option you could try downloading Ultimate Boot CD link text and making a boot CD from your PC which, hopefully, will allow you to boot up the laptop. You should then be able to explore the installed OS to see what is wrong without it being 'live'.
Failing that try to get a CD of the same OS as is installed on the laptop and run sfc /scannow link text - you may also be able to do this if a file called I386 is present by pointing at it as shown here link text - scroll down and read the bit about changing the location in which the 'CD' is searched for.