How can i unlock my daughters W810i "phone lock"(not sim lock)?

Can anyone help PLEASE. I bought my daughter a sony ericsson w810i for christmas. she has taken it upon herself to change or set her own "phone lock code" she has not a clue what it is was or could be. Haw can i reset this phone back to factory settings when i cant even turn it on. My daughter is very unhappy can anyone get me back in good books thanks cs.