Is my computer security sufficient?

[Gardor]

today a friend downloaded a .txt file on my computer and i later looked at it and it said it was about 8.4mb... which is incredibly large for a text file. i did put it into microsoft word and it said there was about 30,000 pages and roughly 1million words if that helps... but i just don't know if there could somehow be a keylogger or virus hidden in that .txt file seeing it was so large.. i use firefox, and when to the downloads window and right clicked the original download, but it did not allow me to open the file or open the containing folder... i deleted it off of the downloads window i did a full virus scan on my computer and nothing came up- i also tried to do a system restore but it told me my anti virus program was preventing it from working. i disabled my anti-virus program and tried it again but system restore still didn't work. i use norton anti-virus. long story short, from the information provided, i would like to know if i could possibly have a keylogger on my computer, how to detect it and how to remove it. thank you very much. thermonex reviews