Beginning dictation.
Here are some things you can try:
does the flash drive work on another computer?
How many flash drives have you tried? What about other USB devices, like your mouse or keyboard?
Have you installed any software recently? How often do you scan for virus?
I would suppose you've already tried the other USB ports.
And also I would suppose you've tried powering off the computer, waiting a little bit and then inserting the flash drive about 3 min. after the system is ready to go.
Please confirm what operating system you are using and whether not you updated frequently. Also, can you give the full model number of the computer you are using?
(This is dictation. Please pardon errors.)