So my sister could not get her flash drive to mount.

She has my old 2007 macbook. The little 4GB PNY flash drive was not recognized in the system profiler or disk utility. I reset the smc. Other USB devices like external hard drives and ipods work just fine. Still doesn't mount. Conclusion: It must be a faulty flash drive.

Or is it?

The flash drive mounts perfectly in my 2011 macbook pro, from which I proceeded to reformat the little guy. But no matter how I format at the flash drive, her computer will still not recognize it in any regard.

So I've ruled out the usb ports and the flash drive as being the problem. Clearly I'm missing something.

What?

Do other flash drives work on your sister's MacBook?

yes other flash drives work as well as external hard drives and ipods.

On that affected Mac try to Reset the PRAM (http://support.apple.com/kb/HT1379) to see if it works when you do that.

I reset the PRAM (restart holding down option, command, p, and r until i heard the second chime)

and it still does not mount