I used to be able to record stuff on my old shitty pc until one night it crashed then I lost all sound and had to reinstall my sound drivers at which point it became impossible to record sound until last month when I got a new all singing and dancing pc.

Try playing a mp3 in winamp and recording it, if you get the same problem it's likely either a problem with your pc specs or it could be you are picking up static from somewhere. Make sure when you record from your media player to disable the sound recording in the sound control panel to make sure that you aren't picking up noise frmo any external devices plugged in. If you can record from a playing mp3 fine but not from the line in then the problem lies somewhere in your equipment.