Solving (almost) any boot problems

After reinstalling a windows in a dual boot environment, GRUB will be deleted because Windows will overwrite any MBR boot manager. The easy solution without hassle is to get a copy of the Super Grub Disk available at www.supergrubdisk.org. This nice tool will help you either reinstalling GRUB or even writing back the MBR of Windows in case you want to to so, so it should actually always be in your CDROM collection BEFORE anything goes wrong. You will be guided throught all steps, so just use it.