I have a couple problems that i can't figure out.

when my issues started, i came here and browsed a bit to see what prelim
stuff i should try. i've run a thorough virus and adware scan, with mcaffee
and spybot/ adaware/bazooka, respectively, i've defragged my hard drive, i've
run a check on my registry and compressed it using Abexo, i've used system
restore. i also picked up process explorer nt.

ok, first problem: DPCs. i have no idea what they are. i tried googling
them, and i mostly got a bunch of jargon that i couldn't understand. i bought
some hardware about a month ago: a usb music interface. for the first few
weeks it was running perfectly. before installation, i reformatted my hard
drive and reinstalled xp pro, installing updates and drivers also. everything
was running fine pre and post installation. then, i brought my laptop and
music stuff to college with me. the first time i tried using it, it begins
working fine, but after a few minutes the CPU usage shoots soars to levels
that prevents the audio from being processed correctly, and slows everything,
including my mouse, to a crawl. i tried restarting the program, and the CPU
immediately drops when the program in exited, and jumps up again when it
runs. i should also point out that the hardware really doesn't do anything
until this basic program is opened. before my problems, my CPU was ~3% when i
was playing.

after trying all the methods i listed above, i finally opened process
explorer while this was happening. the cpu usage for the DPCs are insanely
high, usually between 30 and 60 percent during this slowdown.

this must be the cause of my problem, but since i don't know a thing about
DPCs, i'm not sure how to fix this. i also find it weird that things were
fine until i got to college, though i should mention that i didn't use the
hardware for a few days before and after arriving at college, so maybe
something happened during that time frame. any help would be appreciated.

*deep breath* second question, this one a bit more unknown to me. i've been
experiencing some major slowdown while trying to do a few things at once. for
example, i can usually use AIM and itunes together no problem, but as soon as
i start browsing the web, my comp starts to slow. i've never, ever had this
problem before. virus/spyware scans all negative. specs: P4-HT 2.8 Ghz, 512MB
duel channel RAM, more than 2/3 of my hard drive is free. when this slowdown
happens, process explorer tells me that it's usually two programs using
massive CPU: iTunes and process explorer itself. IE and the Opera browser
will ocassionally do this as well (Opera more so than IE). if i shut down my
computer for a bit, it usually runs fine upon reboot for quite a while, but
it will then slow down again.

i always thought i was pretty decent with computers (even most of my floor
comes to me for help), but i have no clue what could be causing this. i've
tried everything i know, so there's obviously much for me to learn. please
help!

a final note: i wonder if these two problems could be related since neither
happened until i got to college. i've also tried uninstalled everything i
installed since arriving here.

thanks for reading all this,

Matt