When Windows XP tries to load, I get the following message: "We apologize for the inconvenience, but Windows did not start successfully. A recent hardware or software change might have caused this." My options are:

Start in safe mode.
Safe mode with networking.
Safe mode with command prompt.
Last known good configuration setting (most recent setting that worked).
Start Windows normally.

None of these options work for me. I can select any of them and the Windows logo will appear. The screen will go black for a few seconds, then it will turn blue and this message will appear:

Stop: c0000218 {Registry File Failure}
The registry cannot load the hive (file):
or its log or alternate.
It is corrupt, absent, or not writable.

Beginning dump of physical memory
Physical memory dump complete.
Contact your system administrator or technical

and then the computer restarts. Repeat until I shut the computer off completely.

This message only appears for a split second. I had to set my camera to burst mode (to take several pics sequentially) and start the shooting before it even appeared to have a chance to see what it says on my camera.

I don't know what I'm going to do. This laptop is 3 years old and all my files/data are on it.
I recently installed a new program, Peachtree Accounting, on the laptop. I did it about a week ago. Ever since, the laptop ran very slowly at startup. The requirements said at minimum you needed 512 mb of RAM, which is all I have. Now, I cannot even get into my computer :(