2 Hardrive questions

Ok my first question is that about a year ago i had a computer that just crashed and when you started it up it just wouldnt go past the wall paper, and the wallpaper was the only thing you coud see. This happened while i was playing a game online and it froze and i tried to restart my computer and that happened. At that time i had an external hardrive plugged into the computer and what i want to know is that can i plug this into my present computer and it will work fine and not screw this computer up.--My other question is that my present hardrive is losing and gaining space randomly and i don't know whats taking it up. It may be somthing from the internet but i don't know so if sombody could suggest somthing to me that why its losing this space that would be great.

well what game were you playing.... and did you torrent it and save it to tht external? because if you did tht could be a virus and if you hook it up to your current computer without protection it could cause it the do the same

I was playing battlefield 2 and im not sure where i had it saved and right now i have a good virus protection system not, avast anti virus and i also use spybot search and destroy which locates the viruses and deletes them with a scan, where as avast just detects them when they are seen.