how do i use it? ive backed up all my data on a external Ipod so please help its reinstalling windows xp pro

I have Norton anti-virus and spyware.

I turn on my computer and it can't find where to start windows. Is there an app. out there to fix this?

registry cleaner xp?

my system is informing me about critical problems occure in the system and it suggests for registry cleaner xp?how to remove these critical problems that require immediate attention?