Digital BW, The Print

Hi,
First, I am having a problem...
I have a Lexar SD Memory card reader, and a Lexar Card, and I plug 
them both into my USB port. When I go to removeable drive F, it says 
please insert disk. What is wrong???

All my printers and everything work (they are by USB too). And this 
reader/card both worked last week, now they dont.

I know it isnt either the card or reader, because I took the card to 
walmart to get prints made since this didnt work, and it read it 
fine. So I tried again, and it still cant. And the reader is about a 
week old, and worked a few days ago.

What is wrong?

Email me at zacdl@... thanks.

Zac