Q: Macbook Pro really slow after installing OS X 10.10.5

Well I have had a bucket load of problems with it since. (Maybe I should tart a new thread?)

I repaired the disc from the safe start disc utility and then it seems to run bt spasmodically (the computer would intermittently freeze along with appearances of the rotating beachball, but there would be nothing recorded on the console for those periods of time where it was 'frozen'.)

I managed to start in in repair mode (holding down Command-R when hearing the boot up sound) and do a repair to the macintosh HD and get some of the permission repaired, but it seemed to get stuck repairing some of the permissions and it couldn't undo the modification to the SUID file I did when I follow Linc's instructions earlier. (I guessed it wouldn't be able to anyhow.)

So I decieded to see if I could download and reinstall the earlier Mavericks system because it never had any problems running that, but once it had downloaded it from the purchases window, it wouldn't let me complete the installation.

So I decided 'might as well try upgrading to the 'El Capitan' system, because at least that would do a completely new system install right?

It did the download and started the installation, by 1:3ish in eh morning it was running the instal and saying 'estimated time remaining 25 minutes'. By 7am the following morning it was still stuck in eh same position. So I switched the machine off in frustration and now it won't reboot properly unless in safe mode. (It keeps starting to boot but then weird white text in black rectangle-doxxes comes up in lines - over the top of the grey screen with the apple symbol - and then it cuts back to the beginning and does the same thing two more times before it gives up and another symbol appears that looks like a 'power-off' symbol. Anyway I can start it in safe mode (holding down 'Command -P-R') and the Disc Utility dialog box comes up. Should I try reinstalling the system software again? Or should I unmount and re-formatt the whole thing? (I have my data backed up on a Time Machine backup disc)

PS I'm logged in from my iMac desktop computer at the moment.

Hayelp!!

Now when I try and reboot into safe mode it sort of starts funny and the black startup bar (under the Apple icon) doesn't get all the way to the end, and then the startup bar goes blank, and the black line goes back to the beginning end of the startup bar for a fraction of a second or two, and then a 'Language Chooser' menu appears in a menu bar for a fraction of a second, before the 'OSX Utilities' menu appears. Then the when the disc utility window opens I can't select any of the menu items (The 'Restore', 'Reinstall', 'Get Help' or 'Disc Utility' menus). The 'continue' button is greyed out and the pointer won't activate any of the items. (It still activates some of the items in the menu bar).

I've never had so much trouble trying to get Apple software to install on an Apple computer and I've owned Apple computers for 2 and a half decades. This might be the last straw. Once upon a time they used to supply some discs you could reboot from, but there were none in the package when I first bought the computer (which I remember thinking at the time was strange). Anyway seems like a colossal waste of time and money down the drain. I'm really P*ss*d *ff. Don't know what to do.

Okay got a on-line chat session with tech support and got it sorted. Couldn't save a copy of the chat transcript though - otherwise I'd be able to repeat the steps here for everyone

Okay. THese pages are helpful for me in the end

Resetting the System Management Controller (SMC) on your Mac - Apple Support

Try safe mode if your Mac doesn't finish starting up - Apple Support

Eventually this enabled me to get back to where I could erase the hard drive and re install everything

And there's more...

Even though I completely erased reformatted the HD and reinstalled everything I was still having the same problems. Unexplained pauses with no activity on the console. iTunes songs would unexpectedly stop in the middle of playing and then resume again, trouble with installing stuff, updating stuff, switching between programs, opening programs, closing programs. loving off, shutting down etc etc.

Finally gave up and took it to an Apple Service provider (luckily it is still under the extended Apple Warranty). They tested everything and decided the HD was working fine, BUT they found that the cable between the HD and everything else was faulty, and that was causing the problems all along. Turns out that this is a common problem in Macbook pros the technician told me. They have fixed dozens of them by replacing the cable.

So if your'e having these sort of problems, take it to a technician and get them to check the cable. There you go

Incidentally the Technician did confirm that mid 2012 MacBooks did run more slowly on Yosemite. But he did say to try installing El Capitan, because apparently its an improvement, so here goes...

Actually I've decided to stick with Mountain Lion again for the time being. Its much faster - just like new.