USB Flash Drives

Okay, this is getting plain ridiculous. I am now on my fourth USB drive purchase and once again, the USB Flash drive quit working. The first two were Lexar 1 GB JumpDrives and they both come up as unknown devices. Some generic flash drive I got with a cheat device responds the same way. Now the fourth one worked yesterday. Now it's coming up just like the others, as an unknown device. I've tried all of the drives on two laptops and three desktop computers and sometimes they all come up as unknown devices or the comps act like the drive was never inserted.

So has anyone ever had to go through this? Any ideas as to what to do? Tech support doesn't seem to have any so I hope some of you have some knowledge on this sort of thing. Maybe they are defective, if so, then I just have really bad luck. But I need to be sure because I'm getting sick of returning these things. Thanks for any help you guys can give me. :)