You will have to supply more information if you want real help with
this. After using the XP disk did it fix things, does the computer boot
up properly now? If not what happens when you try to boot? Are you
getting any error messages when you try to boot? What are the exact
contents of the error messages?
With the dearth of information you've provided, I don't have even a
remote guess. Start by telling us what "My computer would not boot up
this morning" means. What happened when you tried? If you got an error
message, please quote it verbatim.