I would start off by removing the external HDD from the system and booting up. Try scanning for Malware and Viruses as Facebook (and myspace) is notorious for having malicious advertisements that can render a system unusable.
If nothing is found, try using the computer without the external HDD attached at all as some external HDDs can cause windows to freeze the disk management, which causes windows to not be able to access the master hard drive. It's an odd glitch, it's a random glitch, but it does exist.