My tone dies when I plug into my computer

what is a good, cheap, under 50 bucks soundcard to be able to record in good quality?

ummmm Creative Audigy sound cards a good. also the Creative X-Fi have some good cards but theyre pretty expensive so look on ebay
have a look at some external m-audio sound cards. you generally get better quality with external firewire stuff because they don't suffer static interference from the rest of the components in the computer. M-audio is recommended by Protools but i'm sure there are other brand out there that are similar.