I had two OS,win 7 and Ubuntu, I was working with win and went out of the room and when came back I saw Grub Rescue!!! I booted live and did grub_repaire and it still says multiple active partitions.operating system not found

I feel that it can not find the ubuntu hard drive at all! !

ubuntu@ubuntu:/dev$ sudo fdisk -l

Disk /dev/sda: 320.1 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders, total 625142448 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: 0xde771741

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *          61          61           0    0  Empty
/dev/sda2            2048    30146559    15072256   27  Hidden NTFS WinRE
/dev/sda3   *    30146560    30351359      102400    7  HPFS/NTFS/exFAT
/dev/sda4        30351360   334483299   152065970    7  HPFS/NTFS/exFAT
ubuntu@ubuntu:/dev$ ls
autofs           dvdrw     loop4               ppp    ram5    shm       tty15  tty29  tty42  tty56      ttyS10  ttyS24  uinput   vcsa1
block            ecryptfs  loop5               psaux  ram6    snapshot  tty16  tty3   tty43  tty57      ttyS11  ttyS25  urandom  vcsa2
bsg              fb0       loop6               ptmx   ram7    snd       tty17  tty30  tty44  tty58      ttyS12  ttyS26  usbmon0  vcsa3
btrfs-control    fd        loop7               pts    ram8    sr0       tty18  tty31  tty45  tty59      ttyS13  ttyS27  usbmon1  vcsa4
bus              full      loop-control        ram0   ram9    stderr    tty19  tty32  tty46  tty6       ttyS14  ttyS28  usbmon2  vcsa5
cdrom            fuse      mapper              ram1   random  stdin     tty2   tty33  tty47  tty60      ttyS15  ttyS29  v4l      vcsa6
cdrw             fw0       mcelog              ram10  rfkill  stdout    tty20  tty34  tty48  tty61      ttyS16  ttyS3   vcs      vcsa7
char             hpet      mei                 ram11  rtc     tty       tty21  tty35  tty49  tty62      ttyS17  ttyS30  vcs1     vga_arbiter
console          input     mem                 ram12  rtc0    tty0      tty22  tty36  tty5   tty63      ttyS18  ttyS31  vcs2     video0
core             kmsg      net                 ram13  sda     tty1      tty23  tty37  tty50  tty7       ttyS19  ttyS4   vcs3     zero
cpu              log       network_latency     ram14  sda2    tty10     tty24  tty38  tty51  tty8       ttyS2   ttyS5   vcs4
cpu_dma_latency  loop0     network_throughput  ram15  sda3    tty11     tty25  tty39  tty52  tty9       ttyS20  ttyS6   vcs5
disk             loop1     null                ram2   sda4    tty12     tty26  tty4   tty53  ttyprintk  ttyS21  ttyS7   vcs6
dri              loop2     oldmem              ram3   sg0     tty13     tty27  tty40  tty54  ttyS0      ttyS22  ttyS8   vcs7
dvd              loop3     port                ram4   sg1     tty14     tty28  tty41  tty55  ttyS1      ttyS23  ttyS9   vcsa
ubuntu@ubuntu:/dev$

someone said { Remove the boot flag from sda1, by typing in a terminal: sudo fdisk /dev/sda1 Then press the 'a' key, and 'Enter'. Then press the '1' key, and 'Enter'. Then press the 'w' key, and 'Enter'. } but after grub-repair I got this log:

http://paste.ubuntu.com/1371297/

then I try sudo fdisk /dev/sda1 and But It says unable to open /dev/sda1! which is right as sda1 is not in dev folder (look at the picture!)

Can anybody help me? I need to work on my windows for the rest of the semester and don't care of my ubuntu. thank you