I've got an acer laptop and i have just bought some external speakers.
My built in speaks work..when the other speakers are not plugged in.
The new speakers go in and out of volume but I would suspect it wouldnt sound as bad if all the speakers were working along side them.
If I unplug the speakers the built in speakers work fine. I just wanted the new ones for volume boost.
Please get the problem fixed by changing the speaker settings. For accessing to the Speaker settings, please get to Start> Control panel> Sound and Audio properties> Volume tab> Speaker settings and click on advanced.