So, been having this problem for a while now. Occasionally (once or twice a day), Lion will just freeze up on me and i have to force it to shut down as nothing will respond. After I do this, it will not boot and will sit there with apple logo and spinning wheel for an hour or so. If i do a PRAM reset it will boot up normally, however does not fix the problem. This has been happening since i updated my graphics driver with the latest Nvidia drivers, which is the only other thing I have done besides replacing my Hard Drive, and the problem has persisted even with a new Hard Drive. Since then, I have installed a new hard drive, and done several clean installs, including upgrading to Mountain Lion. Recently, a new problem has emerged as well, my apps in the background such as mail and itunes will crash and i will be unable to re-open them. It says i have run out of space or something similar. Even though I have 128gb Vertex 4 SSD. With abtou 115gb free space. Rebooting temporarily fixes the problem. Similarly, a clean install has not fixed this problem!! Am getting very frustrated and need some urgent help. If anyone can that would be fantastic. Thanks.