ok first off you need windows disks, do you have them? ill assume yes.
before we start, read the last paragraph.
done that?
good, lets begin
now, when the pc starts, it says 'enter setup hit del' or something like that, do that, and try and find something called 'boot order' or 'boot devices', usually under 'advanced settings', once you find it, change the first one to 'CD/DVD'.
now, insert your windows cd, then reboot again.
you will come to a setup screen, and just install! quite simple stuff.
the only thing you will need to do is make sure you format the disk, it should do it on its own if you choose 'format partition'
if it doesnt, delete the partition and carry on.
if all fails...
run setup, then quit setup, then type
fdisk
use this to delete partitions, then start setup again.
once you install windows again, you will notice its really slow, and scrolling is jumpy. this is because windows is using its own 'drivers'. these basically make hardware work.
before you do any of this you need to download every single driver for your laptop and put them on a cd.
to do this, just google your laptop model followed by 'drivers'
there we go, hope it helps