Sometimes in windows partitioning & formating there's a change in partition's number. Eg: /dev/sda3 become /dev/sda4 So if U get on booting an error 17... "cannot mount selected partition"... Fix it like that:

1. On grub splash select the line of your entry and press "e" to edit
2. Change the number of the partition... Ex: (hd0,2) -> (hd0,3) and press "enter"
3. Reboot
4. When you can reboot on your system fix menu.lst with new settings...

Sometimes in windows partitioning & formating there's a change in partition's number. Eg: /dev/sda3 become /dev/sda4 
So if U get on booting an error 17... "cannot mount selected partition"... Fix it like that:

1. On grub splash select the line of your entry and press "e" to edit
2. Change the number of the partition... Ex: (hd0,2) -> (hd0,3) and press "enter"
3. Reboot
4. When you can reboot on your system fix menu.lst with new settings...