I had two external drives failing in the same way. One was a WD, the other was a Lacie. Both network access drives.

They both stopped showing the disk in explorer, but I could retrieve the hard drive and plug them into my computer. With UFS explorer, I copied all the wanted files from the hard drive, with no errors. Then formated the hard drive (the one inside the Lacie box). The WD was more recently and at work, I still have it plugged inside my computer if anyone needs anything from there (which I doubt, since I copied most important stuff already).

The Lacie box actually had a WD hard drive inside, which I still use today as a regular internal HDD.

Now, if they actually show in explorer but you have errors, then maybe it is actually the hard drive failing.

My advice: uninstall CCleaner, copy over the files you need, if you can, and format the drive. If the issues persist, like slow access, error copying files over, do one last thing before you trash it: plug it into a diferent sata port. If it doesn't read well, forget the disk.