Stopping the PC Angel service in Windows - as suggested by PhoneixS - and reinstalling GRUB2 from the live CD solved the problem on my old HP 510 laptop.
Despite of the complicate guides one can find on the web, reinstalling GRUB2 from live CD is very simple. After booting, open a terminal and type:
sudo mount /dev/sda7 /mnt
sudo grub-install /dev/sda --root-directory=/mnt
changing sda7 with the disk partition containing your /boot directory.
Thank you to PhoneixS and everyone else who contributed.
Stopping the PC Angel service in Windows - as suggested by PhoneixS - and reinstalling GRUB2 from the live CD solved the problem on my old HP 510 laptop.
Despite of the complicate guides one can find on the web, reinstalling GRUB2 from live CD is very simple. After booting, open a terminal and type:
sudo mount /dev/sda7 /mnt directory= /mnt
sudo grub-install /dev/sda --root-
changing sda7 with the disk partition containing your /boot directory.
Thank you to PhoneixS and everyone else who contributed.