[ubuntu] Dual Boot Fails

The situation is this:

Windows 7 on its own HD
Unbuntu 12.04 installed after on its own HD also

Although there is an entry in the menu to boot into Windows, it doesn't. It tires and then the screen goes black and the PC performs a warm boot.

Here is the entry in grub.cfg :

<<

### BEGIN /etc/grub.d/11_custom_proxy ###
menuentry "Windows 7" --class windows --class os {
insmod part_msdos
insmod ntfs
set root='(hd1,msdos1)'
search --no-floppy --fs-uuid --set=root 769C03AB9C036549
drivemap -s (hd0) ${root}
chainloader +1
}
### END /etc/grub.d/11_custom_proxy ###

Any hints someone ?

Thanks a million