OK, one step at a time.
What kind of computer are you using ( PC / mac )?
Not that it matters, it's just that I don't know anything about macs.
Assuming a PC:
When you plug it in, is it even recognised by the PC?
Does anything happen at all on the PC? Does it go 'Boop-Boop' to suggest it's found a device?
It takes a minute or 2 to boot and show up on the PC, but then it should show up just like a USB memory stick.
If you go to Windows Explorer, it should appear as 1 or 2 drive letters ( depend if you have an SD card installed ).
Your rides are stored in the X:\garmin\activities folder.
( where X: is the drive-letter assigned to the device. )
There should be a bunch of .fit files in here: these are your rides.
Can you see them here?
They are named according to a time/date stamp.
Is the device just full? Can you just delete older rides?
Now, what websites are you attempting to upload to?
Garmin Connect needs a browser plugin.
What happens when you go to the website?
Does it complain about a missing plugin?
Does it find the device?
Explain exactly what the website is, and what happens.
Use small words, and lots of them. I'm a bit slow.