As @Blender mentioned in his comment this sounds like a hard drive failure. As you don't know Linux very well, I would suggest your first port of call would be to find someone who does as fixing this sort of issue (or even understanding fully) can be hard if you don't know some of the intricacies of Linux.
First use either a Live CD or Live USB stick (see Knoppix as an example or Ubuntu) to boot the machine and see if it can mount the disk(s). If it can, copy the important data off (you should be backing this stuff up anyway but that is a separate issue) and then try and track down what hardware failed. If it is an hard disk then replace it.
You can also look at the logs to try and track down what the issue was in the first place. For hardware I'd check
/var/log/dmesg. Depending on the type of drive (and version of the kernel etc.) you'll see different messages. When the drive is connected to a SCSI/Raid controller you may see messages relating to SCSI commands being corrupt or not being responded to. You may also see messages saying writes have timed out (as another example). It is hard to say what you might see as it depends on hardware and kernel versions.
You can use
smartctl --all /dev/<hard disk> to check on the SMART information. This is built into the hard drive and is the way that the disk can tell you how sound it is.
The JBD error you see is because the EXT3 journal is mangled. If the Live USB/CD distro can't mount the partition because of this you can mount ext3 partitions as ext2 (which ignores the journal) to get the data off. But again, this is something you may need to be a little more seasoned at using Unix to be able to pull off. However, you can do a Google for this procedure and see if you can perform it while booted off the Live USB/CD to allow you to mount the partition.