Ok, I have a big problem right now, my main account on the computer I am using (Macbook 15 inch 2012) is impossible to use. I cannot open any browser or other application like skype, and other applications. It seems to be quite random (other than all of the browsers) which ones do not work. I noticed the "fontd" process running at high amounts of CPU, somewhere around 50% of one core. I then logged out of that account and onto this root account that I had set up in case of an emergency like this. I tried http://dysphoria.net/2012/02/18/mac-keeps-pausing-fontd-run-amuck/ didn't help at all. I gave up searching and shut down the whole launchd process which was above fontd in hierarchy, this somehow allowed me to get one application running (firefox) and it actually worked, of course, that was the only application on the screen and I was unable to do anything until I logged out of that account. I am betting that I will have to figure this out myself by moving around files and figuring out which one is causing the problem, but if anyone has had this problem before and resolved it, please please please tell me.
Also, this occured after I had restarted my computer because one application was not running how it was supposed to be running. I had to actually hold and shutdown the comuter manually (power button) because there was apparently a trash emptying operation going on that had broken (I actually get this a lot, normally not a problem.).
Try setting up another admin user account to see if the same problem continues. If Back-to-My Mac is selected in System Preferences, the Guest account will not work. The intent is to see if it is specific to one account or a system wide problem. This account can be deleted later.
If the problem is still there, try booting into the Safe Mode. Shut down the computer and then power it back up. Immediately after hearing the startup chime, hold down the shift key and continue to hold it until the gray Apple icon and a progress bar appear. The boot up is significantly slower than normal. This will reset some caches, forces a directory check, and disables all startup and login items, among other things. If the system operates normally, there may be 3rd party applications which are causing a problem. Try deleting/disabling the third party applications after a restart by using the application unistaller. For each disable/delete, you will need to restart if you don't do them all at once.