Trouble with Ubuntu and Windows 7 dual boot

I just had a surprising problem with our new Packard Bell OneTwo.   While it had apparently worked fine after installing Ubuntu on a spare partition in the hard drive, I booted it under its original Windows 7 operating system this morning to test benjamin's program with windows.
It worked fine, but after it had been switched off it absolutely refused to boot - no error messages or anything.
Went into the bios settings to take off quite boot and quick boot, but still no errors.
It booted off the Ubuntu live CD ok, and I could mount the linux root partition.

My best guess was that the boot loader was mangled, so I re-installed grub by doing:

sudo mount /dev/sda6 /mnt      [sda6 is my root partition]

grub-install --root-directory=/mnt /dev/sda

 This worked ok with no errors, and re-booting the machine gave the familiar grub boot menu.   Ubuntu booted ok...we'll see if it works after I use Windows next time - I suspect it was Windows that killed the boot loader!