one guess would be a script prob, maybe a dialog/pic window messed up. try typing /remote off
and see if it still happens. (you can turn them back on with /remote on). Is there anything in what you see that could help identify the window that pops up? Is it with all sound file types? Wouldnt hurt to look thru your scripts to see if there's anything there that has splay or sound
Since mIRC doesnt play the sounds, but sends them to windows to handle, can you play those sounds directly in mediaplayer all right?
Needless to say, also wouldnt hurt to run a good virus scan or two especially if you have a script you didnt know you had, like with this one