System impossibly slow

Hello-
I am ruing Ubuntu Trusty 14.04.3 on my HTPC installed on a 2TB hard drive mounted in the front bay. I use it to run Kodi media center and all of a sudden, it has gotten so slow that it is basically non-operational when trying some functions while it seems ok when accessing others. A prime example of this is Addon Installer. Trying to run the add on installer completely shuts the system down causing it to lose coection with my remote and requiring a hard reset. Tried to delete and re-install, just hangs on "Installing add-on..." Dialog box and nothing happens...

There is no problem accessing local media (located on the same drive, for now...). I did a check disk, says the disk is OK and my inteet coection seems fine. My question is, could this be a problem with the drive despite the check disk function saying it's OK? I'm thinking of replacing it with a SSD but don't want to spend the $ if that's not the problem. Any help would be much appreciated, I'm stumped!!!