Used USB with a pc, now doesn't show up on Macbook?

I have a Macbook Pro 13" 2009 running OS X (10.6.8), and yes, I know I need an upgrade. Anyway, earlier today I was using someone's ASUS computer (I don't have any more information except that it runs Windows 7, sorry), and I plugged in a few USB drives (one 4 GB 'Verbatim', one 4 GB 'PNY Attache'), checked the contents, and ejected the drives. I did not modify any settings on the drives (NTSP, FAT-whatever, etc.) when it was connected to the PC.

Now when I plug these drives into my Macbook, the light on each flickers and then goes out. The drives do not show up in Finder, but show up in Disk Utility. I have tried both disks on a friend's Dell HP laptop and they work fine there as well, however they don't on the Mac.

I was reading that drives can and should be formatted/reformatted, but that this erases all the information on the disk. I know very little about the inner workings of computers, just the topical stuff. I considered putting the files on my friend's computer and having her email the files to me, but that doesn't solve the overall problem of the flash disk not working. One of the disks is a back up of all my writing, the other disk contains contents that are not saved to my computer (I just had an external hard drive crash so I am in a tight spot right now and having to use my old usbs to transport files between computers).

I am wondering if there is anything a PC can possibly do that would make these usb drives unreadable to a Mac? If so, then just wondering if anyone has any tips/suggestions for what my next step might be in solving this issue.