Sound Recorded to Computer is Distorted

I have Windows 7 Home Premium 64 bit with a VIA High Definition sound card.

When I record from my record player or cassette deck, all audio coming through the computer is distorted, especially if it's a loud recording.

All the Stereo Mixer and Recording levels are set to low. I'm using an RCA audio/video cable with the red and white ends on the turntable or tape deck, and the other end is a 3.5 mm jack inserted into the microphone jack on the front of the computer. In the sound properties, under stereo mix, the level is set to 54. This doesn't affect the recordings. The next selection is the front mic. The level is set to 10 with a microphone boost of 0. At this low level, most of the entire recording has some level of distortion. I record to WavePad, and the distortion is there EVEN THOUGH the waveform peaks are nowhere near the top.

It wasn't always like this, so I don't know what happened. All the settings seem to be correct.

By the way, I hooked up a new 8 track player I purchased last week with the same setup. There are no volume settings at all on the machine. When hooked to the computer, a volume setting of ONE was enough nearly to blow out my speakers! What's happening here?

Thanks for the reply! I plugged the 3.5 mm into the line in on the back of the computer, and it works without distortion.

However, as I am recording, there is an echo where I hear everything twice. It records and plays like that.

When I start recording, I have to go in to Line In properties and unmute it to be able to record. This is where it starts getting strange. The level in the line in has no control over the volume unless it is set as 0. Then the left channel goes mute, while the right channel stays the same. The levels in the Stereo Mix apparently control the incoming level, though I'm still getting that echo.

Also, the Line In says it is currently unavailable in the dialog box, but it has a green check beside it.

Update:

I disabled the Stereo Mix and changed WavePad from Stereo Mix to Line In. However, all the levels in the Line In keeps going up without me changing them, I have to mute it then unmute it to make the levels come back (otherwise it would stay muted), and I still have that echo.