well. the problem obviously isn't the DSL connection. it pulls in the same internet information that every other internet connection does (with the exception of filtered connections, which would not cause this specific of a problem.
this leave the problem solely on your computer. now, my first recommendation would be to throw it away and build yourself a PC, but that's another topic entirely. backup your stuff, re-format your harddrive, and start over. with stupid random problems like that, the dirtiest solution is usually the best. if it's anything like Windows (i know what you guys are thinking, and i know it isn't) once things start to get messed up like that, it is best to start over. but that is just from my experience. but that's just me. i'd rather spend an evening formatting and re-installing than a week or so troubleshooting in the dark.
good luck