Why can't my computer recognize flash devices?

Clarifications

Try the Flash in another machine to confirm it's working.
Is it listed under Device Manager?
Check if you have any devices that are using the Flash device's drive letter.
Go to (Win7): Control Panel - Administrative Tools - Computer Management - Disk Management
If your device is listed there, try to change the drive letter.

It's a 16GB Flash Voyager from corsair. I have another 1GB Kingston Data Traveler-same problem.
Malcolm

Check that you don't have some network drive hogging the drive letter. This can happen if you are on a network that gives you drives like E:, F: etc. Your USB ports will try to use these but if they are all assigned then the port often gives up and just doesn't load up the flash drive. If this is the case you can go in to the system settings and force the USB port to use a different drive letter. If not, try deleting the ports and let the OS redetect them through device manager. This may refresh any corrupted driver files.

I had the same problem. I tried to change the drive letter. It worked after rebooting but when the drive was removed and reinserted the next time, it would not appear in "my computer". In the end the problem was solved by re-installing the OS (XP). At the same time the unresponding keyboard problem was also solved.