mount error, special device does not exists

mount error, special device does not exists

I have a hard disk of 320 GB on ubuntu 12.04 64-bit.
2 drives of my hard (sda7 and sda8 of ext3 type) cannot be mounted.
output of sudo mount /dev/sda7 /home -t ext3 :
mount: special device /dev/sda7 does not exists!
/dev/ contains the following:
sda sda1 sda5 sda6
but GParted shows sda7 and sda8:
output of blkid:
/dev/sda1: UUID="a898f3ad-11d9-4dbb-9ea8-71a819dc8f70" TYPE="ext4"
/dev/sda5: UUID="998c7c6f-5ff8-426c-83d4-1a309b7cdc4f" TYPE="swap"
/dev/sda6: UUID="da0460d0-714e-40ae-b88b-a0deca87087c" TYPE="ext4"
/dev/sdb1: LABEL="FLASH DRIVE" UUID="8A24-B5CD" TYPE="vfat"
output of fdisk -l:
Disk /dev/sda: 320.1 GB, 320071851520 bytes
255 heads, 63 sectors/track, 38913 cylinders, total 625140335 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: 0x17ea17ea
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 194559 96256 83 Linux
/dev/sda2 196607 625121279 312462336+ f W95 Ext'd (LBA)
/dev/sda5 196608 8007679 3905536 82 Linux swap / Solaris
/dev/sda6 8009728 61431807 26711040 83 Linux
/dev/sda7 61432623 337911209 138239293+ 83 Linux
/dev/sda8 337911273 625121279 143605003+ 83 Linux