Need help with my dual boot

i installed ubuntu on my pc the other day as a dual boot. my other operation system is Windows XP Pro. the first time, after installing ubuntu, i tried to boot up xp, it worked fine. ever since then xp hasn't been booting up....well i can't even tell because my screen is just blank. i have tried loading up the XP disc to reinstall xp but the screen is still black. can anyone shed some light on this situation please. if you know what i should do add me on msn so you can guide me through it please: