possiblly your virus scanner... i had this problem many many times till i figured out what it was... the problem was the virus scanner ... i download large files such as movies n programs in rar or zip format and the virus scanner was set to scan compressed files.. it would freeze up my mirc for a good 5 min till the file had been scanned... dont know if it does it with uncompressed files too.. prolly would, but ive never downloaded a 200+mb exe or media file.. so i cant say for sure...but it sure does sound as if this is your problem

maby thats your problem