Laptop will not boot.

I have a problem with my laptop not starting.

Toshiba Satellite M45 Series Laptop. OS: XP; MS WIN Home (SP2)
Intel Pentium M 730 (1.6GB, 2MB L2 cache, 533Mhz FSB)
512 MB SDRAM, 100 GB hard disk (5400 RPM)

The first times I turned it on it showed the WINDOWS XP screen and the little horizontal bar underneath runs the little 3-light sequence across the bar for about 2 minutes before (1) going to a blank screen or (2) C000218 Registry File Failure Registry cannot open the hive (file) \System Root\System32\Config\Software or its log or alternate. It is corrupt, absent or not curable. Dumped physical memory.

Now it will only go into the SAFE mode screen before going blank. It will NOT recognize the Toshiba Recovery, Applications & Drivers CD.

I tried to open BIOS by pressing DEL at when starting, but it went into the SAFE mode screen & then went blank.

I guess I need a new hard drive? What should I do before buying & installing a new HD? I am a beginner at this & have spent the past 3 days reading to get this far. How do I know it definitely is not something else?

Thanks, Al