Hi all! I am having a very strange problem with my MacBook and will try to explain it as best as I can. If anything is unclear, let me know and I will try to answer. I have a MacBook Pro 13'' (mid 09) and another MacBook pro 15'' (early 09). The problem below applies to both of them. I often use my 15'' mbp connected to a usb keyboard, mouse, display etc. Basically it is used as a stationary computer that can be easily moved (to work/school etc). This is my main laptop so this is where I noticed the problem first. Sometimes when just using the computer as normal (using itunes, opera, adium etc) the OS X will just suddenly become very sluggish and unresponsive. However it is not OS X itself, but the GUI! Example: if I move my mouse over the dock, it wont animate. If I try to do any finder related action the GUI response is way of and if I try to do something in the menubar I have to hold left click, if I let go it just closes the menu. This goes for the application folder as well (I have it as a list). Normally it will just funtion as normal but when this problem occurs I have cant let go of the mouse button when moving through the menus because then the menu closes! However, not only finder gets sluggish, but the whole system. The strange thing is that it is only the GUI, not the applications themselves. Now, this only occurs when the laptop is connected to the above named accessories. A reboot will not fix it, it is still sluggish. Neither is a PRAM reset. The problem vanishes if I disconnect the monitor though. Its a 24'' samsung syncmaster (mini display to DVI connection). Strange huh? The problem only occurs when it is connected to the monitor. I have also managed to get this exact problem with my 13'' mbp. Very strange. Same circumstances as well. What I know is not the problem: Amount of RAM (have plenty left) Bad ram (passes AHT) Display (works perfectly with my dad's uMB 2.4 (late 08) All the accessories work correctly What I suspect might be the problem: I have done alot of experimenting with OS X since I have just been a Mac user for 1 1/2 years (Love it, never going back to the dark side ). I have done a couple of clean installs but always restored my user profile with time machine. I suspect it might be something in my user profile. If I do not restore my time machine backup after a clean install the problem dissappears (however I really dont want to start from scratch). Other info&thoughts: I am running 10.6.4. The computers work flawlessly except for this strange problem. Any help would be gratefully appreciated.