How do I reboot my computer so that I can start new one

I have no idea wgat you mean by this. Do you mean re-install your OS to start fresh or just simply restarting your PC?

Can you explain more about your problem?
Exactly which windows have you installed and is that problem of restarting windows or installing fresh windows.

If you mean that you want to change you operating system you should change your boot order so that it starts up from the cd drive frist and then when it does so insert you new oprating system cd and follow the oncsreen instructions :-)