dual boot - GRUB menu doesn't show Windows 7 option

I'm in need of help to repair my Dual OS (Windows & Ubuntu), I installed Ubuntu after installing Windows 7 but GRUB menu doesn't show Windows 7 option to select.

I'm here to ask how can I make my computer a dual OS boot such that Windows 7 is already installed.

Disk /dev/sda: 40.0 GB, 40020664320 bytes
255 heads, 63 sectors/track, 4865 cylinders, total 78165360 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000abaf4
Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048    74010623    37004288   83  Linux
/dev/sda2        74012670    78163967     2075649    5  Extended
/dev/sda5        74012672    78163967     2075648   82  Linux swap / Solaris
Disk /dev/sdb: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xf449f449
Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *          63   251658224   125829081    7  HPFS/NTFS/exFAT
/dev/sdb2       251658225   503316449   125829112+   f  W95 Ext'd (LBA)
/dev/sdb3       503316450   754974674   125829112+   7  HPFS/NTFS/exFAT
/dev/sdb4       754974675   976768064   110896695    7  HPFS/NTFS/exFAT
/dev/sdb5       251658288   503316449   125829081    7  HPFS/NTFS/exFAT