Reads like you have more problems than the ability to Force Quit. You should only rarely have to rely on that if ever. There are a number of reasons I can think of, but the easiest thing to do is some basic maintenance. BACK UP YOUR DATA!!!!1!!
If you can, get the free Onyx and run the full scripts. That will include repair of permissions. Then reboot twice.
If the problem persists, boot up on your Installation Disk and run Disk Utility to see if your volume is okay. Repair it if not. If you have problems, repair then re-run until no more problems. If you cannot repair, then your volume is frelled and you should consider either an Archive and Install or Erase and Install. The later is only if you have backed up your data--which you should do anyways.
If the problem persists, you can consider third-party repair programs like TechTools and DiskWarrior. However those are more for saving your data.
At this point, if you still have problems you need to consider hard ware problems such as bad RAM. Failing RAM can cause the problems you describe, but it usually also causes kernal panics--screen goes black with gray runic messages that tell you you need to reboot! With the Installation Disks you can run the long hardware tests--there is a "How To" thread on that in the "How To" section coincidentally. . . . I do not know how reliable it is in diagnosing failing RAM, however.
Anyways, start with those. You can also try running Console and posting what happened when programs froze. This will help the Gurus if all of that fails to resolve your problem. There is one who claims "your Mac is screaming at you" in Console--it is just that most of us do not speak the language!
You should also post your full machine specifications: see my signature--Model, Processor, RAM, OS
MacBookPro 2.8 GHz Intel Core i7, 16 Gig RAM, 10.8.5--"Okay . . . I will try Mountain Lion!"
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