Cruzer 8GB flashdrive give message you need to format the disk before you can use it. I selected Cancel because I have work related files on drive and I need to recover. Next message box popped up with "L\ is not accessible. The volume does not contain a recognized file system. Please make sure that all required file system drivers are loaded and that the volume is not corrupted. Can I recover files?
See if running CHKDSK on the drive helps. CHKDSK is run from a Windows Command Prompt.
Example: chkdsk l: /f
You can also try to plug this in on a different computer. Drive L makes me think that you have a lot of partitions set on your computer. Make sure to back up you files too. 
This issue occurs to storage device when file system corrupts or becomes RAW. You can fix it by formatting the disk. If the drive can’t be fixed by formatting, there must be physical problem on the drive. Then you should consider buying a new drive. If the disk contains important files, you need to retrieve data from it and the following steps to recover data from damaged partition.
Recover files from the disk in question:
Step 1: After downloading and installing Eassos Recovery Free, you can double click its icon from desktop to launch it. Then click button “Recover Files From Partition”.
Step 2: Select the drive which can’t be opened and reports error message and click “Next” button to start searching for files.
Step 3: When scanning completes, you can select files and click “Recover” button to get files recovered.
http://www.eassos.com/blog/how-to-fix-the-volume-does-not-contain-a-recognized-file-system/
Format the disk:
Step 1: Plug the inaccessible disk to computer so that it can be detected.
Step 2: Open Disk Management. Right-click Computer/This PC icon from desktop and choose “Manage”, and then click “Disk Management”.
Step 3: Find out the RAW drive and right click it to select “Format”.
Step 4: Set volume label, choose file system type, allocate unit size, select “Perform a quick format” and click “OK” button. Wait for a second and formatting completes.
I have faced the same problem when I used the SanDisk SD card to be connected with my computer yesterday night, a prompt popped out same as yours: You need to format the disk in drive before you can use it. I was afraid if I click the formatting button, everything on the SD card will be wiped, however, after clicking the Cancel button, there’s still a prompt: F:\ is not accessible. The volume does not contain a recognized file system. Please make sure that all required file system drivers are loaded and that the volume is not corrupted. I entered to the This PC and could find the SD card still exists, but it was shown as 0 bytes after right-clicking the properties.
I didn’t face such problem before, hence I tried to find solutions from Google, and they said I need to confirm whether the SD card is still showing in Disk Management or not (in this way: Press Win Logo key+ R and type “Diskmgmt.msc”) and I can see the SD card there.
All right, I am willing to share the full steps of how to get back my precious photos from my SD card and the exact steps to fix this issue step-by-step to help others who have the same problem like me and the topic starter.
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I installed Bitwar data recovery software, it can detect the original file system of the RAW disk. e.g. my former file system of the SD card is FAT32. The software can display the disk type like this: FAT32_RAW. Then the software can provide Quick Scan mode for me to get back the photos with original file name and folder structure.
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After getting back the photos, I then formatted the disk to make it normal. However, there are still other methods to fix the error, you can check here in this article to know more. (https://www.r-datarecovery.com/drive-is-not-accessible.html)
Hope the answer can help most of you, Good luck!
