I upgraded ram recently to 28GB of RAM now freezing and crashing.

Not really.

The only correct, compatible and reliable Mac RAM can ONLY be purchased from online RAM sources Crucial memory or OWC (http://www.macsales.com).

OWC is a all Mac specialty company.

If the RAM isn't working, it is not working. Macs are PICKY about the specs of the RAM. If the specs of the RAM are not right or slightly off, especially the timing latency ( has to be below 11 ns), the RAM can be problematic.

PNY is more of a PC RAM manufacturer as Windows PCs are more forgiving of lesser spec'd. RAM

You are going to need to replace the RAM.

Even it you can get the RAM you purchased to function in your Mac, the existing RAM you installed will only cause your Mac issues later down the road.

Replace it with RAM from Crucial RAM ( directly from their website, NOT from Amazon.com) or from OWC(macsales.com).

Do you have the original RAM still? You can put that back to test although I agree that the RAM will need to be replaced. You can also run the hardware test (see link - or use Diagnostics depending on your model). Now, does PNY offer a warranty? If so, return it as not compatible.

Using Apple Hardware Test - Apple Support

28GB is a strange configuration. Did you leave one of your original modules in because without it the iMac wouldn't boot? If so that indicates incompatible ram.

Sorry meant to reply to the OP......haven't done that in awhile 😕 but since I did.....babowa, shouldn't the modules in any one bank match?

PNY RAM is trash!!!!!!!

I had put it into a late 2013 27" iMac when I first got it.

Even the "Apple expert" at Best Buy said it would work just fine.

Well, when I got it home got all set up and put the RAM in, all seemed okay.

However, after a while I would encounter some occasional app instability

and on some a few times a kernel panic.

When Yosemite came out and I updated, the situation was even worse.

Daily app crashes and every so often kernel panics. Was ready to throw

Yosemite and my iMac out the window.

I then recalled seeing threads in the past where such issues happening

after an update were caused by crappy RAM.

I bit the bullet and purchased new 32 GB upgrade from OWC. I put it in

the iMac and it has been totally free of any issues ever since and is operating

trouble free as a Mac should.

Do yourself a favor, trash the PNY RAM and get good quality RAM.

I'm not sure with the latest configuration - vertical slots where OEM RAM is usually in slot 1 and 3 from the top although I've seen posts where it's in 1 and 2. FWIW, having it in slots 1 and 3 equals the "old" side by side configuration of matching them horizontally. Did I explain that right?

In any case, I would always match them either horizontally or 1 + 3 and then 2 + 4.

And, no problem - I figured out whom you meant to reply to. 🙂

I'm waiting to hear back from him, I'll bet he had to leave one of his original 4gb modules in to make the mac boot.....that should have been cause enough to return it before his window of chance closed.

This iMac (27-inch, Late 2012 and later): Installing or replacing memory - Apple Support seems to indicate his configuration is ok, just incompatible bargain basement ram.

Static from ones fingers can fry memory modules