If using the 1/8" line input/output on the average computer, chances are the 1/8" jack just "failed" - likely the solder joints gave out. They are really not meant to do much with(Sad but true). While it should be an easy fix for someone who knows how, it would be better to get an actual sound card, made for actual use. You can buy a nice one for 100 dollars(US) and up(Way up!). Sound cards are the same, but different... When you're looking them over, you can, for instance, throw-out all the ones that DON'T have the connectors you need. If you start at the top of the range and "throw out" all the ones that "don't fit" your needs(Too pricey, too cheap, too many inputs, too few outputs, whatever), you'll soon end up with just a few to choose from(I ended up with only one, how convenient, which is in my machine and working beautifully.).

TG

It might also be likely that the Windows mixer has been hijacked and changed by some other program?

Every sound card has its own mixer program and most of them suck and are confusing. I recommend you use the Microsoft mixer instead of the one included with your sound card. They work in parallel with each other and I find the Microsoft mixer is cleaner and more straightforward to use. All Microsoft Windows operating systems already have a mixer program built in. You can find the Microsoft mixer by going to your start menu, "programs", "accessories", "entertainment", and finally select "mixer". The mixer you see now is not the recording mixer. It is the playback and monitor mixer. To get to the recording mixer, you drop down the "options" menu. Then you select "Properties" and choose "Recording", followed by "OK". You will now be looking at the input selector and recording mixer control. Select line input and you may discover that there is nothing wrong with the input connectors or sound card?

Mixer madness
Ms. Remy Ann David