Starting up problem on my pc!

Hello,
i use my pc desktop almost every day (it runs on windows xp). it was working fine until this morning. I turned everything on, the hardrive worked fine however the monitor comes up black with white writing "saying pheonix 2007" it tells me to press f1 for setup, after this it says press f10 so i did & by accident entered "network boot". my computer then starts up normally after i click on network boot. I can use everything & it works as normal but im not sure why i get this problem in the begining. I have no idea what to do, could some please help out!