Bootloader of XP is corrupt. Insert the XP CD. Goto repair option, provide your admin password so you can get the c:\ Then type the following in order,
fixmbr
bootcfg /scan
bootcfg /rebuild
fixboot
This should fix. If needed, try the same in 7 too.
I do this many a times, once after installing Vista, once after installing Paragon software, which created some bootloader with no options
Try it and let us know.