Ubuntu – Swap not available on System Monitor

I had a swap partition of 1GB (RAM 1GB, Ubuntu 12.04 lts). Now swap is not shown on System Monitor neither can I hibernate my pc (sudo pm-hibernate).

blkid output:

/dev/sda1: UUID="B8B4FBB1B4FB706C" TYPE="ntfs" 
/dev/sda2: UUID="2ea7d608-2d89-4e41-9436-d05cb3ce8871" TYPE="swap" 
/dev/sda3: UUID="3219d03a-67e4-454b-8ce7-a27831846e35" TYPE="ext4" 
/dev/sda5: LABEL="Softwares" UUID="AC1CC3301CC2F47C" TYPE="ntfs" 
/dev/sda6: LABEL="Education" UUID="1E103E6C103E4B53" TYPE="ntfs" 
/dev/sda7: LABEL="Recreation" UUID="2CC8D181C8D149AA" TYPE="ntfs" 
/dev/sda8: LABEL="Miscellaneous" UUID="0274D6B174D6A727" TYPE="ntfs" 

/etc/fstab

# <file system> <mount point>   <type>  <options>       <dump>  <pass>
proc            /proc           proc    nodev,noexec,nosuid 0       0
# / was on /dev/sda6 during installation
UUID=3219d03a-67e4-454b-8ce7-a27831846e35 /               ext4    errors=remount-ro 0       1
# swap was on /dev/sda5 during installation
UUID=2ea7d608-2d89-4e41-9436-d05cb3ce8871 none            swap    sw              0       0

free -m

     total       used       free     shared    buffers     cached
Mem:           991        867        123          0         27        418
-/+ buffers/cache:        421        569
Swap:            0          0          0

cat /proc/swaps

Filename                Type        Size    Used    Priority

fdisk -l

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders, total 312581808 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: 0x9f369f36

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *          63    31471334    15735636    7  HPFS/NTFS/exFAT
/dev/sda2        31471616    33470447      999416   82  Linux swap / Solaris
/dev/sda3        33472512    62539775    14533632   83  Linux
/dev/sda4        62541045   312592769   125025862+   f  W95 Ext'd (LBA)
/dev/sda5        62541108   125066024    31262458+   7  HPFS/NTFS/exFAT
/dev/sda6       125066088   187591004    31262458+   7  HPFS/NTFS/exFAT
/dev/sda7       187591068   250115984    31262458+   7  HPFS/NTFS/exFAT
/dev/sda8       250116048   312576704    31230328+   7  HPFS/NTFS/exFAT

swapon –all

swapon: /dev/sda2: swapon failed: Invalid argument

dmesg | grep -A 5 -B 5 -i swap

[    9.487404] EXT4-fs (sda3): ext4_orphan_cleanup: deleting unreferenced inode 131645
[    9.487413] EXT4-fs (sda3): ext4_orphan_cleanup: deleting unreferenced inode 131330
[    9.487418] EXT4-fs (sda3): 16 orphan inodes deleted
[    9.487420] EXT4-fs (sda3): recovery complete
[    9.578600] EXT4-fs (sda3): mounted filesystem with ordered data mode. Opts: (null)
[   20.580539] Swap area shorter than signature indicates
[   20.588363] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready
[   20.619443] udevd[330]: starting version 175
[   20.649959] lp: driver loaded but no devices found
[   20.662972] [drm] Initialized drm 1.1.0 20060810
[   20.675515] i915 0000:00:02.0: setting latency timer to 64
--
[   72.288573] PM: thaw of drv:sr dev:3:0:0:0 complete after 178.143 msecs
[   72.288578] PM: thaw of drv:scsi_device dev:3:0:0:0 complete after 178.136 msecs
[   72.299677] PM: thaw of drv:scsi_device dev:2:0:0:0 complete after 189.270 msecs
[   72.309473] PM: thaw of devices complete after 202.763 msecs
[   72.309668] PM: writing image.
[   72.309670] PM: Cannot find swap device, try swapon -a.
[   72.309699] PM: Cannot get swap writer
[   72.329896] Restarting tasks ... done.
[   72.331777] PM: Basic memory bitmaps freed
[   72.331792] video LNXVIDEO:00: Restoring backlight state
[   72.420048] option1 ttyUSB0: option_instat_callback: error -84
[   72.804047] option1 ttyUSB0: option_instat_callback: error -84
--
[  145.960625] sd 7:0:0:0: Attached scsi generic sg2 type 0
[  145.972036] sd 7:0:0:0: [sdb] Attached SCSI removable disk
[  172.430508] PPP BSD Compression module registered
[  172.455583] PPP Deflate Compression module registered
[  332.260789] type=1400 audit(1381814763.342:27): apparmor="DENIED" operation="capable" parent=1 profile="/usr/sbin/cupsd" pid=636 comm="cupsd" pid=636 comm="cupsd" capability=36  capname="block_suspend"
[ 1913.030998] Swap area shorter than signature indicates
[ 2022.530155] type=1400 audit(1381816453.610:28): apparmor="DENIED" operation="capable" parent=1 profile="/usr/sbin/cupsd" pid=636 comm="cupsd" pid=636 comm="cupsd" capability=36  capname="block_suspend"
[ 4062.729509] Swap area shorter than signature indicates

Please help. Thanks in advance.

df -h

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda3        14G  6.1G  7.0G  47% /
udev            488M  4.0K  488M   1% /dev
tmpfs           199M  868K  198M   1% /run
none            5.0M  4.0K  5.0M   1% /run/lock
none            496M  224K  496M   1% /run/shm