Without more details, it's impossible to say what's wrong, much less how to fix it. First, though, you should understand that the partition table type (GPT, MBR, APM, etc.) is independent of the filesystem type (ext2fs, ReiserFS, FAT, etc.). If you have no entry for the partition device file (/dev/sda2 or whatever), then the problem is most likely in the GPT data structures. If you can "see" the filesystem but not repair it, then the problem is almost certainly at the filesystem level and not in the partition table data structures. Thus, you should begin by posting that information -- do you have device entries for your partitions? You should also post the output of the following commands:
parted /dev/sda print
Change "/dev/sda" to your disk device and "/dev/sda2" to the partition that's giving you problems. (Obviously, you won't be able to use the fsck command if you don't have the relevant device node.)
oussena, I recommend you start your own thread; your problem may have a very different cause and solution to gac's problem, and trying to solve two problems in one thread generally creates confusion.