Fast then Slow

[josephjohnson5]

Desktop imac ran great for about a month, than it really slowed down. My drive was anything but full. Everyting seemed to check out, but it was extremely slow. It took about a hour to boot up completely. And during that process nothing responded. Even clicking the mac start button would freeze the computer.
So I erased 'Macintosh HD' and downloaded Yosemite. Once again, it worked great for two days before it totally slowed itself up again.
I've tried this process many times. Nothing seems to work. Any ideas?
Computer Specs:
Name: iMac
Model id: iMac 12,1
Processor: Intel Core i7
Processor speed:2.8 Ghz
Number of processors: 1
Number of cores: 4
L2 cache per core: 256 KB
L3 cache: 8mb
Thank you guys so much!

 

[honestone]

From a hardware perspective, this is somewhat baffling, given that the internal HD spins at 7200 rpm. And, with the machine being less than 4 years old, one would think the hard drive is not failing. What needs to happen first is to check out the HD.

So, first of all, please let us know how you erased the drive. I suspect you used Disk Utility for that, but there are some options in Disk Utility that some don't realize are there. Additionally, how did you run Disk Utility to erase the drive? Also, it would be better if you can do that externally. And, it would be super if you have a more robust Disk maintenance/repair program, like Disk Warrior or Tech Tool Pro.

Next, even with that information, it might be good to start over again. What you will need is the Recovery HD partition on your HD. That is a hidden partition that (usually) gets created with an OS installation. To see if it is there, launch Disk Utility, and click on the Debug menu (it is the next to last menu choice, on the right, next to the one that says Help). Near the bottom of that menu, you'll see "Show every partition". Move the mouse pointer to that, click on it (to "activate" it), and you should see the results of that action right away. You will subsequently either see or not see the Recovery HD partition on the list of hard disks/partitions in the left hand side. For example, I have both my internal drive (a Samsung 256 gig SSD) and an external 1 TB drive attached to my Mac Mini, and for the internal SSD, it shows 4 partitions. One of them is Recovery HD.

If that partition is not there, it can be created a couple of ways. You'll need a copy of the Install OS X Yosemite file to create it. It is usually located in your Applications folder, but it disappears after an OS installation. That is why it is a good idea to have one (or more) copies of it somewhere else. If you no longer have it, you can download it from the Apple store.

In any event, give us an update on this information, and we can help you further.