Experience A 'strange' Heavy-load

From some time ago, this system which characteristics you can appreciate at my signature, it feels very slow and when checking the monitor of the system, effectively it shows a heavy load on 1 of its cores, as you can appreciate in the above screenshot. This is a quad core processor.



When it reaches the desktop right after getting logged, there begins the slow-motion problem. I don't know what could be causing this slow-down. Is there a way to determine the cause of this issue ?

This is a linux problem, I have also installed Windows XP and Windows Vista here. And in any of both systems this problem has appeared yet. <_<

BTW... I'm coming from solve an annoying sound problem as exposed here. I dont think it could be any relation between both problems right ? <_<

Maybe you've got beagle indexing running? Turn it off. Dunno about your slow graphics though.