dual boot Windows 7 / Ubuntu 13.04 issues

[Gerhard Magnus]

I want to dual-boot Windows 7 and Ubuntu 13.04. The computer has 3 hard 
drives, one of which is solid state. I had Windows 7 installed on a 
250GB partition of sda when the box was built, and I have an 
installation disk for it. I then installed Ubuntu on the other two 
drives: /home and a swap partition on sdb, and / on the solid state sdc. 
I put the boot menu on sda.

The Ubuntu system is working fine and is extremely fast -- it's 
obviously using the solid state drive. My problem is that Windows 7 
doesn't show up on the grub menu.

I wish I could completely ditch Windows -- but people I collaborate with 
use Word, and LibreOffice isn't quite a clone and has never caught up 
with Word's group writing and reviewing features.

Here's the abbreviated fdisk -l output:

Disk /dev/sda: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders, total 1953525168 sectors
Disk identifier: 0xb6e884cd
    Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1  1953525167   976762583+  ee  GPT

Disk /dev/sdb: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders, total 1953525168 sectors
Disk identifier: 0x00046867
    Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048  1949420016   974708984+  83  Linux
/dev/sdb2      1949421568  1953523711     2051072   82  Linux swap / Solaris

Disk /dev/sdc: 180.0 GB, 180045766656 bytes
255 heads, 63 sectors/track, 21889 cylinders, total 351651888 sectors
Disk identifier: 0x00000000
    Device Boot      Start         End      Blocks   Id  System
/dev/sdc1               1   351651887   175825943+  ee  GPT
WARNING: GPT (GUID Partition Table) detected on '/dev/sdc'! The util 
fdisk doesn't support GPT. Use GNU Parted.

gparted gives conflicting detail about sda (the Windows 7 drive):
Parti-  File        Mount       Size  Flags
tion    System      Point	
-----------------------------------------------
sda1    unknown                 128MB msftres
sda2    fat32       /boot/efi   100MB boot
sda3    ntfs                    250GB	
sda4    ntfs                    681GB	
unallocated unallocated         2MB

The /dev/sda1 entry has a red "!" leading to this warning:
Unable to detect file system! Possible reasons are:
-- The file system is damaged
-- The file system is unknown to GParted
-- There is no file system available (unformatted)
-- The device entry /dev/sda1 is missing

Has anyone worked through a similar problem or have a suggestion about 
how to proceed?