Rescuing a jfs partition

[Dr Croubie]

So the other day, while I was merrily working, my power supply crapped out on me. Not sure what happened but I heard a click and the computer went dead. Couldn't turn it back on. (The next day, when unscrewing it to fix it, I just thought I'd try it 'one more time' and it worked, maybe it realised I saw that the warranty on it was still valid so it decided to work again). When it rebooted it went through all the usual 'replaying transactions' on the Reiser partitions

Either way, computer works again, except for my JFS partition.
I have the following fstab:
/dev/sda1 /boot ext2 noauto,noatime 1 2 (64MB)
/dev/sda2 none swap sw 0 0 (512MB)
/dev/sda3 / reiserfs noatime,notail 0 1 (32GB)
/dev/sda4 /mnt/virt jfs user,exec 0 0 (25GB)
/dev/sdb1 /home reiserfs noatime 1 2 (1TB)
/dev/cdrom /mnt/cdrom auto noauto,ro,user 0 0

sda is a 60GB SSD, sdb is a 1TB storage disc.
/dev/sda4 I partitioned off when I installed, to practise with Virtualising.
When I installed VirtualBox, I decided to give JFS a go (because I've always used Reiser, and thought I'd better investigate a change in case Reiser goes obsolete without me knowing, like OpenOffice and SunJava have recently)
On it was just one file, a VirtualBox image, installed on that was Vista (which I need for my scanner and printer).
When it crapped out on me, I had Vista running, scanning my latest negatives.

Now, on boot (and when I try to manually "mount /mnt/virt", I get the standard error:
"mount: wrong fs type, bad option, bad superblock on /dev/sda4, missing codepage or helper program, or other error."
dmesg gives nothing useful (or nothing at all). I've double-checked the Kernel and I do have JFS inbuilt and jfsprogs are installed (they must be, because it was working before, but checked anyway).

Any suggestions as to why it's just suddenly crapped out? Any file-recovery tools I can try to get my Vista image back?
(It's only a virtual machine so there's nothing terribly important on it, just installed programs and some downloaded icc profiles, but still I'd rather save it than not).
Thanks

[666threesixes666]

you need to emerge jfs-utils or jfs-tools or jfs_utils or jfs_tools. then run fsck.jfs /dev/sda1&& fsck.jfs /dev/sda3 && fsck.jfs /dev/sda4

er ur errors sda4....

fsck.jfs /dev/sda4 && reboot. it will load fine next boot. id do it from a live use drive distro. i "try xubuntu" and repair from there, its got jfs tools in, because its installer media

[Dr Croubie]

I was thinking fsck, but I thought that it didn't work if the fs wasn't mounted.
but yeah, just tried it anyway and it worked, thanks.

(meanwhile, I think I've found the reason the power supply crapped out, I've got a home-made watercooling-setup with a 240V aquarium pump, via a relay switched using 12V from a fan-connector. The relay was sparking to the pc case...)
(I've also just seen that fsck wasn't set in the fstab, fixed that too)