trojan DNS changer- sound problem

oke, this is my first time asking help but i really don't see how i could solve this anymore:

It all started with a trojan DNS changer infection. I tried to remove it with malwarebytes but that didn't work so i tried combofix. Big mistake, cause it got my pc stuck in a loop saying "nltdr.com is missing, press CTRL-ALT-DEL".
I had no other option of letting my built in PC-restore revert to previous machine settings for windows (the factory revert). I got to keep my data-files, but all my installed programs needed to be reinstalled as the settings in windows were gone.

The problem however is not gone . I don't see anymore trojan DNS changer problem but now my sound card won't function anymore. In de device management window, it shows a yellow exclamation mark and it says the driver is not installed. If i try to update the driver, it run into an error saying "an IO computation was interrupted or a thread was terminated".
The second part of the problem are the windows updates. The updateservice won't get past the activeX you have to install before checking the updates. I think this is related to the trojan, but it could be yet another seperate problem.

I really need some help wih this one, the sound card is my biggest problem. Will anyone please help me??

some info:
windows XP home edition, SP3
sound card realtek AC 97, built into HP Pavilion t652

PS: im not sure if this is the right section, it was either this or the driver section, but the driver is a result of...