everytime i close down my browser a block box appears for a few seconds i can only read the words download c file in the text before it vanishes it has never appeared,does anyone know if it is a problem or how to get rid

internet browser? Try a virus scan to see if anything dodgy comes up, i dont really know enough on computers to give you a full analysis, im sure someone on here will though!

try some anti spyware/anti virus sw

Google for housecall, This is an online virus and trojan checker, completly safe, free, and runs online

when that is finish, search for Spybot search and destroy, run that from your hard drive