Windows XP SP2 Constantly Rebooting!!! URGENT HELP!!!

Ive looked EVERYWHERE!!! its been talked about like crazy here, but im a musician i need of desperate help

My comp just keeps rebooting everytime i start it up, i cant even access safe mode, it just restarts and restarts, i dont have the original winxp cd, cause my lab never came with it, and i dont wanna loose ANY of my files by doing a system recovery, and i KNOW there has to be a way to get this fixed, so please i beg of you, can someone help me??? :[