Windows XP turns to Windows VISTA?

Hello,

I have other problem again, One time I opened my computer and then theres a window pop up asking for the password with corresponding username.. <-- everytime i open my PC but my pc is not like that before... it automatically open direct to my PC.

and other thing, I just change my destkop background and then the next day i opened my pc "It change to somewhat like Windows VISTA" but my pc is using Window XP... now im trying to return on its originall setting the way i used my computer before.. NO USER NAME and PASSWORD asking on my pc everytime i reboot my pc or restart and NO Windows VISTA log or background. (But i know im still using XP its just some logo change to VISTA and i cant go back to its original theme)

If someone here understand what im trying to say.. pls message me if u need more infos about this..thanks again!! hope to hear from anyone of u soon...

More power!