OS boots up then when done loading restarts

[turbo187]

I have a computer with windows xp on it. it boots all the way up but when its done loading it restarts itself automatically. i put my windows xp disk in to start all over again but for some reason it wont read on start up. i went into bios and set it to start cd but got nothing. i tried to due a system restore in safe mode because thats the only thing that works but it wont let me. i also tried configureing from last know good startup but that also failed. i need suggestion because im running out of patience.