Personally, my cheapish USB3.0 to IDE/SATA adapter does allow for SMART info but as has been said, not all of them do.. You could, if you have a USB flash drive free, create UBCD or DLCBoot drive, launch some tools after swapping the HDD into your AIO (if it's easily accessible and you won't kill some kind of warranty!) or..maybe have an old laptop to hand you could pop it into and boot the aforementioned USB or even burn a CD with UBCD/DLC? Or have a friend that can pop it into his/her machine? It does kinda sound like your HDD, i'm beginning to suspect my own is...less than healthy, shall we say xD
As for Crystal Disk Info.. It's alright for free but on DLCBoot the program "Victoria" is available and for older HDDs in particular it's more informative and can give you a much clearer answer with health bars and whatnot..
If you need a hand just let me/us know.. Only being 120GB, might be time to bite the bullet and get hold of a bigger drive for it anyways? If it's not dead, of course..