xp pro vista 64 dual boot

i have xp pro installed on first partition C:/ drive.second partition D:/ i have installed vista 64.at first all was ok, pc would boot to screen asking which operating system to start.for the fist day or so it would boot to choice screen fine.now when i boot up i get "NTLDR IS MISSING,CTL ALT DELETE TO RESTART.so i created a boot disc off my other pc and boot into xp pro from floppy ok.trouble is i can no longer boot into vista.how can i resolve this.

May be changes to boot manager (BCD) settings. A common cause for message about NTLDR missing is change in designation of XP boot location.
"garbea01" wrote in message

i have xp pro installed on first partition C:/ drive.second partition D:/ i have installed vista 64.at first all was ok, pc would boot to screen asking which operating system to start.for the fist day or so it would boot to choice screen fine.now when i boot up i get "NTLDR IS MISSING,CTL ALT DELETE TO RESTART.so i created a boot disc off my other pc and boot into xp pro from floppy ok.trouble is i can no longer boot into vista.how can i resolve this.