So this is a Windows specific thing, but if you have never experienced the Blue Screen of Death, then consider yourself a rare breed. This term refers to when Windows crashes and reveals to the user a completely blue screen with an error code and message stating something to the effect of "something really bad happened and we couldn’t fix it, so we are just giving up and you need to restart your machine while praying that it will boot up all the way." Again, I am paraphrasing, but this is what it looks like:

If you should encounter one of these, your best bet is to try rebooting and hopefully your machine will start up fine. If it does and you can't duplicate the error, then it was probably a fluke. If you can induce the error by reproducing the actions leading up to it, then you should avoid doing those actions if possible. If not (i.e. they are caused when you try to open a program), try uninstalling/reinstalling, doing a system restore, or just repairing whatever seems to be the cause. If your machine doesn't load up properly, then you will have to do some Googling to see if others have shared your same symptoms and error. You might find someone's suggestions in a message board somewhere that can help resolve your issues. Alternatively, you will have to do a system repair or reinstall to get things working again.