Nevertheless, I began encountering a few more problems over the last few days, such as Windows Explorer crashing every time I clicked "New Folder" in the period of a few hours. Computer also "froze" again without the external hard drive attached. Made me think maybe the computer's just gone crazy on its own whenever I open or do something that may take up plenty of memory/CPU. (Opening really old videos with crappy resolution = no problem. Opening today's 720/1080p videos, even those downloaded from Youtube = problem within several videos.) So, hopefully I could get some advice to see if it's anything I can quickly fix on my own regarding the OS before jumping back to the conclusion that my laptop is infected with something.