How old is your comp/laptop, when was it built? Also, maybe a bit more than 50GB, honestly, I freed up 100 GB of crap I didn't need.
Ok, so your computer is probably good. I think it's a software related thing. Anything that interferes in the background, get rid of any un-needed processes in the task manager to use up less CPU to run better. Try that and if it doesn't fix the problem, I may have to examine more deeply.