Classic problem nothing to do with the PC manufacture, rather a registry hive is corrupt in this case it's the SYSTEM hive (You have Windows XP ), there is a backup of this file under %Systemroot%\repair which you can replace the corrupted file with (Thats the one thats in (config\system) by RECOVERY CONSOLE, HOWEVER this backup file is created when the OS was installed and so some software etc will need to be reinstalled.

You are unlucky in the fact your system hive is corrupted, the method above is for retail installations NOT OEM, if you replace the SYSTEM hive on an OEM installation, I.E the PC you brought from the shop, you may not be able to log back into the recovery console again, this is due to the system hive creating passwords and accounts that did not previously exist. (I can bypass windows security though )

Here is Microsofts KB for the issue http://support.microsoft.com/kb/307545, let me know if you have any questions, need help etc. For an end user in this situation I recommend you are best of backing up your data and doing a clean install.

Microsoft actual recommendation is ASR Automated System recovery, however most user's don't do this.

Martin