ubuntu : remove grub mbr

last week i have to format my desktop which is windows XP, ubuntu dual boot to reinstall xp i put windows xp disk in drive and what i see, after booting blank screen nothing happen,i tried 2-3 times but same problem,
windows disk is working in other computers.Later i realized that grub is problem,i have searched internet the solution and finally i got a solution that  doesn't need to full format or erase entire disk you need to remove master boot record (grub) and windows cd will work absolutely fine.
boot in ubuntu or ubuntu live cd.
and use dd command

sudo dd if=/dev/null of=/dev/sda bs=512 count=1


dd command is used to backup one drive to other 
raw copy low level copy etc


detailed description:


sudo : to  run command as super user in ubuntu

dd : dd command

if=/dev/null   source to be copied  which is null


of=/dev/sda   destination /dev/sda is your hard disk ;sda for sata disk

bs : size of 512 bytes is to be written (MBR is first 512 bytes of hard disk which contains boot record,partiton table etc) 


This command is saying that copy 512 bytes of null to first hdd or simply erase MBR.




reboot and boot from xp cd it will work fine.