Why Is My Computer Running Slow

My computer has been running *extremely* slow lately, and even after countless removals of files, it is still running *very* slowly. Then, a thought popped into my mind; I leave my USB, which has *a lot* of information stored on it plugged into my computer 24/7. Would doing that cause my computer to slow down?

Hi i got this virus that make my entire computer slow down. Also, it has pops up randomly even i am doing nothing. When i press ctrl + alt + del and i clicked on process tab, the explorer.exe takes like 90% of CPU. So i have to end process it. Now i have to use new task in task manager to run any programs. I used mal ware bytes and it scanned and killed many of them but it still slow. Help!