One other thing to mention would be that there are tons of counterfeit SD cards on the market, and unless you got yours from a very reputable seller, there is a chance that it is hacked to report a higher capacity then it has.
The comment you made about being able to navigate the file system, but not open anything past 30g is pretty close to exactly how those counterfeit cards behave. I would be surprised if they used a 32g card as a base for the hacked card, but anything is possible... Anyhow, try H2testW, a google search will turn up download links. It is a free program that will write data to a target device until it fills the device. Then it will attempt to read it back and verify it's contents. After a certain number of mismatches, it will report the memory as likely defective.
This saved my butt a few times on some SDHC card purchases. It takes quite some time to run, especially with large drives, but the big plus here is that it verifies the flash memory before you put it in a device and loose a bunch of data that might be irreplaceable.