The first step in the link above requires the winxp cd-rom ! and you left yours home!!
1. Insert the Windows XP startup disk into the floppy disk drive, or insert the Windows XP CD-ROM into the CD-ROM drive, and then restart the computer.
Click to select any options that are required to start the computer from the CD-ROM drive if you are prompted to do so.
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This might work worth a try .
Q: \WINDOWS\SYSTEM32\CONFIG\SYSTEM is corrupt. HELP! (#3546)
A: Your system displays the error message.
Windows could not start because the following file is missing or corrupt: \WINDOWS\SYSTEM32\CONFIG\SYSTEM
That means the System Registry Hive has become corrupted.
There are two ways to get back up and running. The easy way which doesn't always work, and then there is the hard way.
Easy Way --- Note that this doesn't always work.
When you are booting your system, press the F8 key during the start of the bootup sequence, meaning after it does the Power On Self Test.
Once you press the F8 key, you will be taken to a Menu. Select "Boot Using Last Known Good Configuration".
It will now attempt to load Windows XP using a past set of configuration files.
If that doesn't work, there is the next step....the hard way.
The hard way is same as described in the microsoft link in above post