Broken headphone jack on an acer aspire, windows 7?

Well I was sleeping my mom was on our laptop using the headphones and one of our cats jerked the cord, now the headphones will only work if you hold the cord just right and even then only one ear works and the built in speakers aren't working at all, what it seems like to me is that something on one side of the inside of the jack got crushed and now aside from that obviously not working I suspect that it's telling the computer that the headphones are still plugged in even when they're not, I've already done a little research and found the possibility of getting a USB headphone adapter, so what I want to know is (1) is there a way for me to disable the headphone jack so that hopefully the built in speakers will work, (2) will the USB headphone adapter work for my particular problem and (3) will there be any conflict between answers 1 and 2.

Additional Details

First just to clarify everything sound related (in fact everything in general) was working just fine until the cats jerked the cord and broke the headphone jack, this is a fairly new computer and this is the first thing to go wrong with it.

Also I tried GreyHawk's instructions on how the set the speakers to default, speakers was the only option and it seemed to already be set to default. I thought the fact that the headphones didn't show up there might mean I was wrong about why the speakers aren't working, so I plugged in the headphones and held them just right so that the one ear was working and looked again as I was listening to music coming from one ear of the headphone and there was still only the one device and it was labeled speakers but it indicated that that was the device that was being used.