output feeding into new track

what the heck

I have been cruising along since last december recording different songs each with several tracks. today i cranked up n-track and when i recorderd a new track, it also contained what i was playing along to. in other words–if i muted all of the other tracks and only play the new track (one guitar solo) i hear all of the other tracks also.
my sound card recorder mixer will now only record my guitar if the mixer is set to ‘stereo mix’ whereas it use to be set to ‘line in’. now if i set it to line in, i get no action on the record vu meter. if i set it to ‘stereo mix’, the record vu starts to jump and i can tell it is going to record not only my input instrument but also the playback tracks.
i don’t have a ‘record what you hear’ setting on my soundcard. it is just a generic ‘realtek ac97’ that came with my computer.
if someone can help i would sure appreciate it.

Thanks all but nevermind…i did a system restore to a few days ago and now i’m setup ok again. dont know what the problem was but its gone now. i think it had somethinig to do with my MIDI experimenting (re: other posts) :D