Tried to install Windows, and now can not boot Ubuntu partitions - Error Loading Operating System

view story

http://askubuntu.com – i have one hard disk and two operating systems Ubuntu and Lubuntu. I wanted to install Windows XP also but i had only two partitions. I used GPARTED to resize partition with Lubuntu to get more space for new partition. After that i rebooted and wanted to install XP on new partition. But I could not choose that new partition, also i tried to delete it and create again, i didn't touch partition with Ubuntu and Lubuntu. As this didn't work i couldn't choose this partition i decided to restart and see if i did mistake somewhere in GPARTED. But after restart i get "Error loading operating system" (HowTos)