Martine,
Oh, yeah. If you leave the little plastic cap open, they will go bad. You have to keep them sealed up always.
If you put the strip in the meter, and the screen goes blank before you can get the blood droplet, just take the strip out and re-insert it. The screen will light up again.
If those two issues are not possibilities, I am wondering if you got a bad pack of test strips. If you would like, and you are not too far away -- like over an hour in bad traffic -- I could come over and try to help you today (or tomorrow). If that doesn't work or you are far away, I would suggest that you take the strips back to Wal Mart, and ask to exchange them. They are expensive enough that if they are that difficult to use, you should at least try to get a new box. I think Wal-Mart would let you take them back. Not sure. If you get a bad meter you have to send it off to the manufacturer.
I sent you a PM with my phone number in it.