Mandriva won't boot .....HELP

hi everybody ....
yesterday i switched from ubuntu to mandriva ...i downloadded the mandriva one 2009 kde version and installed it on my hard drive along with xp (xp first then mandriva)after completion of mandriva installation it says to halt system then remove live media and to restart ..i did but the system freezed at the splash screeni waited for 15 min but nothing ..i tried reinstalling but same thing ...i powered down the laptop when it freezed ..on reeboot only xp boots no sign of mandriva ....plz help

When I installed Mandriva it installed GRUB, and that (I think) manages the boot-up. It's supposed to ask you which system you want to boot into.
I was asked during the installation where I want to install the GRUB. I don't remember what I picked, but it worked. Every time I booted up I was asked if I want to boot Mandriva or Windows.
I know this isn't too helpful, but maybe a reinstall is what's needed. You haven't had a chance to do anything yet, right? So, no data lost, only time.

At the end of your installation you are asked about bootloader (Grub) installation. You can install it to your Linux (Mandriva) partition or to the master boot record. If you install to the mbr, Grub will usually detect your windows system and put an entry there for it as well as Mandriva. Since you can boot xp, I assume you did not install Grub to the mbr. You have two options (at least):

1: Put an entry in the windows bootloader file, see this link for instructions:

Linux.com :: Convert a Windows system to dual-boot Linux on a second drive
(I've not used this myself so I can't guarantee it but, it looks pretty straightforward)

Re-install Mandriva or re-install Grub. To be able to advise you on how to install Grub we will need your partition information so, insert your Mandriva installation CD and let it load into RAM, then open a terminal/konsole window and log in as root (su) and enter the command 'fdisk -l' (do not include the quotes, put a space after fdisk and that is a lower case Letter L). Post output here.