2 days ago I reboot my computer and when I turn it on, it ask me" windpwsxp(rebooted)" or windows xp. I always have to put reboot because if I put the second option "windows xp" it loads but the computer screen stays in welcome. How do fix the computer to start normal without putting "reboot" every time I turn it on?

Any changes that either happened or that you perhaps made to your computer around the time that the problem started; particularly any Software or Hardware that you installed or setup.

You have to change the boot.ini file, in this you can set windowsxp ( reboot ) option as default to boot your computer automatically,
For step please check this link
How to Use and Edit Boot.ini in Windows XP (http://vlaurie.com/computers2/Articles/bootini.htm)

Check the bios