Since you mentioned the size coming up as something odd, there's a small possibility that Windows is confusing the iPod with another storage device. As a test, shut down (power off) your computer and disconnect all USB devices. You can leave standard USB keyboard/mouse connected, if used. If your computer is a laptop, connect its power supply so that it's not running on battery power. Do a Reset (restart) on the iPod.
Learn how to reset your iPod - Apple Support (See section iPod with a click wheel)
Start up your computer, run iTunes, and connect the iPod to a direct USB port on the computer, by itself. Is there any difference?
I assume you already tried doing a Restore on the iPod using iTunes, but if you have not, do a Restore (in case the cause is data corruption on the iPod). This erases the iPod, reinstalls its software, and sets it to default settings
Use iTunes on your Mac or PC to restore your iPhone, iPad, or iPod to factory settings - Apple Support
If the problem still returns, the most likely cause is the hard drive becoming unreliable.