|The header says "XP Home Edition won't restart after updates"|
If these updates are after installing xp and then going to Microsoft to get updates then you may have corrupted a file.
This does not happen often but it does happen. All is well until the 36 + updates have been downloaded and installed.
Then the computer wont reboot!
HP's had a continues reboot after service pack 3.
Some Dells and systems have their graphics driver screwed up.
If the above applies go into safe mode and reinstall corrupted drivers...
If the above does not apply, hit f2 and see if the Hard Drive and cd rom are being recognized.
If not, are both HD and CD rom on the same ribbon cable?
If so disconnect the power to the cd rom or hard drive and retry. If the one that is still connected is shown then you most likely have have both set as master devises.
It is also possible that the OS on the hard drive is corrupt.
The boot sequence is in the Bios and can be changed
I wonder if the cd rom is actually able to read the cd.
Hope the above gives you some ideas.