The usual cause for missing NTLDR
Is a problem with the hard drive or the file system. Look over this trouble shooting guide: http://pcsupport.about.com/od/findbyerrormessage/a/ntldrmissingxp.htm
I do not see a model number for this HP computer, but most have a key indicated on the HP splash screen for entering the BIOS and for Recovery. First try looking into the BIOS to see if the hard drive is being detected and set for first boot device.