Finder can't recognize USB drive
You could try finding the drive using Terminal. If you're not hip to Terminal commands, the way to access your USB via the command-line is

Open up Terminal, and enter the following commands (hit return at the end to execute):

cd /


This will take you to the highest level folder on your computer's hard drive. Then, type:

ls  


This will list everything there. You should see an entry there called Volumes. Now go into the directory and list its contents:

cd Volumes
ls


The USB's name should be listed, since you said DiskUtility sees it.  

From there, you can browse the stuff in your USB, and use open [filename] to open things.

Otherwise, you might want to copy everything off of the drive and reformat it. That fixes most problems.