I have a Dell Vostro 1720 laptop that originally came with Windows Vista. I have installed Windows XP on it and all the drivers, everything works fine. I constantly Hibernate my PC and once a week reboot it.
Suddenly sometimes the MBR gets wiped out, with no apparently reason I can understand.
I have on the other partition PClinuxOS installed and when the MBR gets wiped, I cannot access that neither. Using the Windows cd to do a fixmbr does not help.
When booting from live cd and trying a Restore MBR or trying through the Control Centre, it says bootloader not found and when installing it the dialog suddenly disappears and the MBR is not installed.
This happens due to the fact Windows was still hibernated.
Use the windows cd to perform a fixmbr
Close the Windows installation instead of hibernating it.
Boot from live cd and Restore the MBR
It took me months to notice this and I always left linux for Windows, hopefully this helps others