I knew before, that i should first install windows and then Linux, but windows tends to have an annoying have-to-reinstall-to-fix-a-problem “feature”.
Luckily the solution is simple. All you need is a live CD distribution with which you boot into your computer and reinstall GRUB (probably also Lilo – I don’t know because I don’t use it). I use System Rescue CD. It works with other LiveCD as well, but System Rescue CD was made for exactly this (kind of) job. It is a command line distro.
First run grub:
#grub
grub>root (hd0,2)
In my case (hd0,2) means 0 for the first (and only) disc in my computer and 2 is the partition number where my grub configuration files are residing (2 means the third (3) partition!!).
grub>setup (hd0)
hd0 in this case also means the first disc in the computer.
grub>quit
Reboot computer and you will see your familiar grub boot prompt.