Hello Missknowall. I am afraid but once you start a diskcheck, there is no way you can stop it unless you manually shutdown/reboot the machine. You could do that but be advised, that it will almost certainly kill your hard drive. Sometimes people get lucky and the hard drive works but that is not always the case.
That is some good news. Considering the status of your disk, it might be difficult to recover data off it later.
There are plenty of reasons for hardware failure. The most common being cheap parts used in the manufacturing of products. There is not much we can do to safeguard ourselves against it.
Again, if you are ABSOLUTELY desperate, you could try a hard restart and hope that the computer still works. However, if you can still wait a while, then try and wait for Neville or Randy or Frank to come on. They are much more competent than me in such matters and should be able to guide you well.
Hope that helps. :)
-- Goku