Hi Gibbs,
When the boot menu is displayed that means that boot manager(bootmgr) is in place (e.g. first disk, active partition) and BCD is in place and is readable. So no problems with boot related files.
If "BootMenuPolicy" is set to "legacy" (0) the booting stops and just boot menu is displayed waiting for user to select a boot entry.
If "BootMenuPolicy" is set to "standard" (1) then we have a preloading of OS files (winload.exe is loaded and executed which loads kernel, kernel boot drivers, eventually antivirus program).
You can change the value of element "BootMenuPolicy" of default loader (should be Windows 8.1) to "legacy".
This can be done using bcdedit from Windows XP (just copy bcdedit.exe from VisualBCD package to Windows XP, bcdedit must be from Windows 7 or Windows 8, bcdedit from Windows 8.1 cannot run on Windows XP).
bcdedit /set {default} bootmenupolicy legacy
You should also place back "hiberfil.sys" to Windows 8.1 partition. (delete only after you have disabled hibernation from a running Windows 8.1 and rebooted)
When you reboot you can select Windows 8.1 boot entry and then after typing "F8" key you will have access to advanced boot options - try booting to safe mode which loads only basic Windows 8.1 modules.
If you cannot boot to safe mode - try
1) "Automatic/startup repair" using Windows 8.1 DVD (should be run 3 times with rebooting after each run)
2) If Automatic repair did not fix booting to "safe mode" try offline sfc (System File Check)
If you still cannot boot Windows 8.1 post outcome of steps you executed (automatic repair, sfc).