Vista - Games stutter now when before they didn't.

Hi all, I have recently bought a new computer. During the course of the last few days, I have begun to install (and remove) programs and apps that I use on a daily basis. Most are games that I have installed. When I first installed Assassins Creed, it ran like a dream. Now however a few days after the install, I am encountering hiccups... almost as if the game is attempting to pre-cache world objects or sounds. Essentially any contextual sound being played will cause the game to stutter and lock up for a microsecond. How do I correct this issue? I know the game ran perfectly for the first little while, but what is the issue now, and how can I reverse it? I have installed so much stuff on the comp, that now it would be almost impossible to determine which did what, and when. System restores have failed to recover my machine from this, and I would love to hear any suggestions on how to attempt to resolve this.

I am running the sound off of the ATI card, because right now my home theatre isn't hooked up to receive the TOSLINK cable from the soundcard. Disabling the ATI onboard sound and enabling the XONAR DX card doesn't help either. I'm suspecting a software or corrupt file somewhere may be the culprit, but some extra input and advice would be welcomed. I have also heard that a reinstall of Windows Media PLayer may be in order, but I have not been able to find a current version to allow me to do so.

You're right in newer computers there is no uninstall for WMP so you should already have WMP 11 have you tried the k-lite codec.That usually works for any WMP problems.

Download K-Lite Codec Pack
I would download the full version which and the 64 bit

TOSLINK? Is everything connected properly?

Thanks Blue for the links. I'll get back to you here once I get them installed and tested.

@frostmourne... I don't actually have the XONAR DXs' SPDIF output hooked up through the home theatre's TOSLINK input (using the cards' adapter)... yet. I have disabled the soundcard presently to ensure no conflicts would happen. I haven't hooked it up yet because my basement is being renovated and ultimately that is where everything is going to end up. Right now, I have just hooked up the GPU's card to the TV using the HDMI cable, but am having these issues with sound/graphic stuttering regardless.

32- and 64-bit versions.

Can you uninstall the game, defrag your drive, run malwarebytes just to be safe and reinstall the game?

4870X2? Get the newest drivers. That card has excellent potential but without drivers a 5870 is faster.

Okay I installed both versions of the codec packages with no result; same thing. GPU drivers are up-to-date as well (v 8.65). Also attempted the uninstall and defrag too (though not concurrently with each other - defragged while the game was installed), no differing result. I'm beginning to suspect it may not be hardware OR software related, but possibly a memeory leak within the game... I'm hearing it becomes increasingly power-hungry and laggy as the game progresses (which would explain why it DID play smoothly at one point in time). When I get a bit more time I will uninstall and defrag, and then report back here again.