There's numerous reasons that Windows won't boot but hard to say without knowing of what has been done to the pc before it's last shutdown. If your HD stopped working then it usually say it can't find a working HD to boot from, and the only time I remember seeing nothing but a blinking cursor and no other info is momentarily when I switch in and out of SLi and during the process of turning off the csrss.exe and that could be bad in your system. Could be memory probs. Listing anything and everything you remember changing before it's last shut down while working would help, hardware or software settings.
