Frequent (at least once a week) system crashes

[40mile]

I have a Mac Pro running El Capitan 10.11.2 and Safari 9.0.2. I am experiencing repeated crashes where either screen goes dark and freezes or there is wild flashing that will not stop. When this happens, only alternative seems to be power off and reboot...HOWEVER in most instances reboot process seems to be clobbered..may take NUMEROUS attempts at "option" backup reboot or "command R" to get system back on line...OS has been reinstalled numerous times with NO positive results...HAS ANYONE ELSE EXPERIENCED THIS PROBLEM???...IS THERE A FIX???

 

[simonsi]

What machine? TBH sounds more like a hardware problem.

 

[40mile]

What machine? TBH sounds more like a hardware problem.

What machine? TBH sounds more like a hardware problem.

MACHINE: iMac (27-inch, Mid 2011)

Problem occurs while browsing...cannot detect trigger or how to capture error...when it occurs I cannot recover without powering off machine...THEN i usually have problems rebooting...most attempts end in machine rebooting itself...sometime have to use "option" key many time before even seeing backup boot disk and even then reboot may fail...same for "command R" ...I am not a system tech so recovery for me is EXTREMELY hard. Have been using company KROMTECT to help me through worst cases but they only treat the problem NOT find the solution.

 

[Ebenezum]

I agree with simonsi, it sounds like a hardware problem.

Shut down the iMac, then start it while holding D. It boots into Apple Hardware test, run the extended test. If it finds problems post the error code.

 

[40mile]

Ran extended tests...NO ERRORS

 

[Gochugogi]

A similar thing happened to me today, but while cloning a drive in CarbonCopyCloner. Couldn't boot into recovery mode and was stuck on a black screen. I have a clone of the internal HD on an external SSD, so I plugged it in, figuring my Mini i7 would recognize a system disk after restarting but to no avail. Finally, I held down the option key at restart and was able to manually choose the external drive as startup. I ran Disk Utility and it repaired the internal drive (took two tries) and all is back to normal for now.

I've suffered similar crashes about once a month after upgrading to 10.11 so I keep two bootable backups of my system drive. Two of the crashes were so bad I had to reformat the drive and copy the clone drive back to the internal. Mavericks was a much more reliable OS. I still run it off an external SSD for certain apps and it never crashes...

 

[maflynn]

Try downgrading it Yosemite and see if that increases stability. Usually frequent crashes is caused by some sort of hardware failure, yet it could be some issue with the El Cap. Downgrading will help narrow down where the problem exists imo.