virius

hi i need some help with this one.i think i have a virus on my
computer.i am running xp pro.
the error says task manager has been disabled by your
administrator.there is a white screen can not do nothing.try to
reformat will not let me boot by my cd.can i put in new hard drive and
try to reboot using my windows xp cd? stumped on this one.been workig
on computer for a lone time.