I'm going to ask a couple of questions for myself and Gary's information and then give you some links to other forums with discussions of the same problem that you're having.
1. Did you install windows 7 as a dual boot with another Operating System? Since you mention drive B: and I see this on other forums with dual boots this may be your problem since Windows usually looks at drives A: and B: as floppy drives. What is on drive C: on your computer? See discussions here:http://goo.gl/U81gl and here: http://goo.gl/tQvGg
(look at post #8, for example)
2. Are you running Kaspersky? See mention of AV issues here: http://goo.gl/WXSeL
Based on the discussions on the other boards it seems to be related to either multiple drives with Windows 7 not on drive C:, dual booting, the AV program, or drivers. If reading the discussion boards doesn't help you please post back with the particular details about your system. Since you stated that it "quit working" it appears that a recent change to your system may have triggered it. Perhaps the change messed up the drive letters? Please let us know what changes--hardware, software, or both--you may have made just prior to the trouble so that we can see if advice for System Restore, sfc /scannow, or drive letter managment would be appropriate as next steps.