I'm with frubes on this one... back up ASAP, but you might also want to check this out: http://forums.pcworld.com/index.php?/topic/64582-helpassistant-folder-keeps-appearing/ There's some nasty stuff that gets into your MBR and causes your HDD to thrash constantly.
Also how often do you defrag your hard-drive? I fragmented files and folders can sometimes cause massive slow downs, especially if you haven't defragmented in ages. And don't bother using the windows degrag tool - utter rubbish. Try get something like diskeeper. And once you start using a defragger, use it at least once a…