Q: Full screen apps error

Hello,

I have MacBook Pro from 2011 (15inch), processor 2,2 GHz Intel Core i7, 10GB memory and OS X Yosemite.

Lately, it happens to me quite often that while working with Safari, Outlook, Adobe or other pretty common programs, my computer "twiches" and in a second the screen devides between two full screen app - usually dashboard and my main screen. And there is a big black stripe between them which I cannot pass with cursor. So let's say 20% of the dashboard is on the left side of the screen, then 10% takes the stripe and 70% is the main screen. So obviously, no screen is complete. But I can move my mouse and work on both. To get from the right side of the screen to the left, I have to move my mouse to the right until I get "out" of the screen on the right and it pops on the left screen (dashboard) on it's left and the same way I can go back - going to the left, I get "out" of the screen and the cursor pops up on the right.

I can usually work like this for a few seconds or minutes and then the spinning wheel of death appears and I do force shut down. Then when I turn the computer back on, it is alright.

Ah and btw, the four fingers movement on the touchpad doesn't work when it gets to the error point.

I hope I explained it ok and someone can help me to fix this or at least tell me what I need to get repaired.

Thanks in advance.