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I would remove Avast, a Google for &quot;mac avast slow down&quot; indicates the problem.<br />
Mac Model? 13&quot; or 15&quot; 2010, 2011, etc &nbsp;The hard drive cable fails on some 2010 to 2012 MBP. Symptoms can vary widely.<br />
Google &quot;macbook pro hard drive cable&quot; &nbsp;I have replaced 7 or 8 in the last three years.<br />
<br />
Create a new user in System Preferences and login as the new test user (administrator) and test.<br />
<a href="https://etrecheck.com/" rel="ugc">https://etrecheck.com/</a>&nbsp; is a good diagnostic tool <br />
Booting with &quot;D&quot; key will run Apple Diagnostic &nbsp;<a href="https://support.apple.com/en-us/HT202731" rel="ugc">https://support.apple.com/en-us/HT202731</a>
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Also, try resetting the SMC and PRAM.
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Try to update mac os via Safe mode and it fixed the issue at the end.
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I had this question after viewing <a href="https://www.experts-exchange.com/questions/24121381/MAC-frozen-with-spinning-wheel.html" rel="ugc">MAC frozen with spinning wheel</a>.<br />
<br />
Just suddenly we discover that our mac start giving us very hard time ( before it was little bad), but all of sudden yesterday as soon as we reboot the pc to turn on, the mac turned ON ok, but following things were happening<br />
1) On clicking applications, they just looks like they opening but they won't<br />
2) after every few minutes, screen goes black, and after pressing slightly power button, screen comes back but with spinning mouse<br />
<br />
So far we able to do following things<br />
1) Run PC in safe mode, <br />
2) Go to disk utility and run disk first aid repair ( something like that)<br />
3) Run Avasta AV scan ( left for whole night, but in the morning can't see where it finished)<br />
<br />
Please assist us
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I had this question after viewing MAC frozen with spinning wheel (https://www.experts-exchange.com/questions/24121381/MAC-frozen-with-spinning-wheel.html).

Just suddenly we discover that our mac start giving us very hard time ( before it was little bad), but all of sudden yesterday as soon as we reboot the pc to turn on, the mac turned ON ok, but following things were happening
1) On clicking applications, they just looks like they opening but they won't
2) after every few minutes, screen goes black, and after pressing slightly power button, screen comes back but with spinning mouse

So far we able to do following things
1) Run PC in safe mode, 
2) Go to disk utility and run disk first aid repair ( something like that)
3) Run Avasta AV scan ( left for whole night, but in the morning can't see where it finished)

Please assist us

Mac book pro running forever spinning busy icon, mouse moves but no use, keep going to black screen

iOS is a mobile operating system developed by Apple; it is a derivative of the Mac OS X desktop operating system, with which it shares many (but not all) common frameworks and other components. These include Cocoa Touch, the Mach/Darwin/XNU kernel and code from the Berkeley Software Distribution (BSD). Each iOS application runs in its own secure sandbox to prevent altering other applications, the operating system, or any other data.

Apple's early computers ran on a variety of operating systems, including a Pascal version and one based on CP/M, before releasing its ProDOS with the advent of its 16-bit computer. With the release of the Lisa, which had its own OS, Apple and computing entered the graphical age; it was followed by the Macintosh, which offered a series of "System" operating systems. Other Mac operating systems included PowerPC until Apple acquired NeXT and folded it into the Mac OS. Current operating systems for Apple devices are Mac OS-X and iOS.

Apple OS

Mac OS X is the desktop operating system from Apple Inc., found on Macintosh computers. OS X consists of a Mach/BSD-based kernel, operating system interfaces primarily based on FreeBSD and additional frameworks (written in C, C++ and Objective-C providing user interface and application-level services.