Beware of good deals on large memory cards. Fakes are a lot more cleaver than you think - and fool very smart people. Here's my own experience:
128 GB Memory stick on eBay, $35. Should have been my first clue that something was amiss.
USB stick arrives. It's in name brand packaging. Looks like I just picked it up at BestBuy. Must be legit, right?
Plug it into the machine. Machine says 128 GB. Neat, must be legit, right?
Being extra cleaver, I reform it on my computer. Takes several hours. And my computer says it's 128 GB. Must be legit - right?
I transfer over about 2 GB of data, and they read/write/etc just fine. Must be legit, right?
Over the course of time, I use a bit, everything works good. Must be legit, right?
A few weeks in, I transfer over about 4 GB of data. It transfers over fine. The files show up when I click on the card. The data files even run when I double click them. Must be legit, right?
WRONG! The card is a fake, and passes all these tests. It's actually only a 4 GB card. After I exceed about 4 GB (on my "128" GB memory stick), AND try that memory stick on another machine, it doesn't work. In fact, almost all the new data is corrupt, and doesn't actually work.
Know why? Because it's a FAKE.
Here's how it works.
What they do is take 2, 4, or 8 Gb memory and at the factory hotwire it to report that it's actually 128 Gb, or whatever size they want it to say. Windows just assumes that hotwire is legit, and doesn't actually do it's own real check. And when you reformat it, Windows happily reformats it acting like it's a 128 GB memory stick. And if you transfer data to it, up to it's real size, why everything works fine.
The real fooler is, when you copy over more data then that (i.e. more than 2 GB in my case), and then double click on the data files, why they open up just fine. They do so, because Windows apparently is going back to the original location on you HDD to actually run it. That last test is what really tricked me. It's repeatable, because the bastards got me 3 times before I did the on-line research to figure out this is what they are doing and how it works.
Eventually I was able to reversed all the charges on them via the credit card (don't waste your time with PayPal, they'll just jerk you around).
So if you get a really good deal on large memory. My advise, fill it up immediately, then take it to another machine, and test if everything you transfered over actually works. Here's betting it doesn't. And most people don't do this - at least not for a while. So the unscrupulous on-line suppliers keep on selling them, knowing that 95% of the customers will just assume it went bad, or they got it wet, or maybe never notice at all.
Don't know if this is the OP's issue, but bewarned on buying a "good deal" on memory on Ebay.
And while I'm at it, the cheap Mexican "pure natural" vanilla, is fake too. It's artificial.