monitor screen changes

Thank you!
It is intel pentium III, windows xp professional.
When i start it, the monitor displays a blue or white screen , then stops there until out of power. What might be the problem and how can i solve it?

Another problem is that it has a lot of virus and infected files, i want to format it? But i can’t seem to find the option of booting from disc, on which site can i find its drivers.
Thank you once again!