Connect the USB stick in the USB port of your computer.
WAIT for the computer to recognise the stick. In some cases, it can take around a minute.
Open the explorer (assuming a WIndows PC).
Does the USB stick show? Can you see it's content?
If you don't see the stick, try in another computer, desktop or laptop, Mac, PC or Linux, it don't mather.
If it don't show, it may be dead. Try conecting it to another port or another computer. If it don't work on another computer, then it's dead, good for the recycling bin.
If you can't see the content, then it's file system is probably corrupted:
Right click it and sellect "Format".
Any content will be erased, the file system will be reinitialised to a clean state.
The USB stick is now ready to use.
If formating don't work, try formating on another computer. I have a stick that appeared dead on 2 other computer. I formated it on my computer, and now, it can be used on any computer.
If, after all the above, it still can't be used, then the stick is realy dead. Replace it.