Vista won't boot after xp shutdown


EasyBCD dualboot xp & pre-installed vista on Acer Timeline.
So far xp works fine. At shutdown xp will do completely the task until the laptop turn off. When I turn on it back every time vista will not boot, I got only progress bar back & fort without end.
What is the problem? Is easybcd the problem or something else?
Any help?

Vista works fine after repair. If I choose xp to restart, vista will boot up properly.
Just never click xp shutdown, otherwise vista need to be repaired again.
Any idea, What is wrong?
How did you install XP ?
Can it see Vista ?
If so it will certainly be destroying Vista's restore points and shadow copies.
Can it see Vista as C:\ while it is some letter other than C:\ ?
If so, applications you install on XP will possible have corrupted files on Vista, by defaulting to the C:\ disk instead of the XP partition.
Xp is installed on d: drive in logical partition. It can see and write anything to pre-loaded vista in c: drive. I installed some applications on xp & vista as well opera, firefox, ms office, firewall, antivirus etc. It looks like everything ok, I can not say much, my son use the laptop for school & he will come back in winter break.
I think, that reg tweak will solve the problem. Thanks for the link & support from you all.
Do a search through the XP registry for "C:\" and note any apps that have put things on C.
They'll fail when you make C invisible to XP.
Uninstall them all before you do the hack (on Vista too if you installed them there too - Adobe reader, flash etc will all be mixed up)
Then reinstall them on both systems after XP can no longer see a C:\ disk, and they shouldn't clash in future.