Seconded circumstantial evidence
Unfortunately, I can second madisonwi's statement. I realize that sufficient time has passed that this message will be of use to the original poster, but people (like me) are still having this problem come up, and I believe it's worth keeping the issue alive.
I have had *two* of these Toshiba 6100's die on me, under similarly mysterious circumstances, in as many months. The first one periodically threw up this request for a "BUILT IN HDD PASSWORD =", but rebooting several times would eventually result in a successful boot. After about a week of this message periodically appearing, the hard drive grunted spectacularly and never functioned again. That is to say, it died as a hard drive normally dies, being inaccessable on boot and unmountable as a secondary hard disk.
The second one (1st symptom) threw up a documented
Blue Screen of Death on boot, and after several reboot attempts allowed me into safe mode, where (2nd symptom) a chkdsk /f turned up a shit-ton of errors, before eventually informing me of an "unknown error" which caused the machine to lock up tight. A reboot put me into Windows with no trouble. The next reboot gave me the dreaded (3rd symptom) "BUILT IN HDD PASSWORD =" request, where the hard drive sits today. Useless. Ruined.
Both of these series of events proceeded as a normal hard drive failure would proceed - only the second instance ended with a t-totally ****ed drive. Like madisonwi said, this is well-documented everywhere
except the toshiba support website