What file are you trying to open? It sounds like Windows has lost associations to files.
That was a very good description.Most of the time disk 1 is the Operating system. What he means is when you boot from the XP CD it will go throught a file check the you will be prompted to press enter to continue or R to repair. Choose enter to continue, then you will be prompted to press F8 to approve of the EULA, go ahead. After that XP will do a search for previously installed windows, if all is well you will see C:\ windows XP "Press R to repair" this is the R you want to choose if you do not get this option then it means that you Operating system is corrupted, which means you will have to reinstall windows xp. "Hope this helps"