Honestly since you just installed I'd say wipe and reinstall from scratch.
id say you have no idea how much that makes me want to /cry ... but im guessing you actually do.
Also I highly recommend downloading one of the Windows 7 rollup packs (make sure your disc installs SP1 at least) and the prerequest KB as well that way you can install all (the vast majority of) your Windows updates from those two, also do them while offline, so it doesn't do that bug where it tries to find updates for several hours.
not sure what a rollup pack is or how to go about that. The first time tho it didnt take all to overwhelmingly long to run updates. Just a few restarts.
Edit* read up on this. Seems basic enough.
Or if you want (since your PC is halfway decent now) make a vmware player VM of windows 7 and give it like 2-3GB of ram (if you have at least 8) and install XI in that. That way it's sandboxed, that's how I play and somehow I manage to avoid most of the crashes that others have.
i have no idea what that even means honestly. The only thing i ccan say to that is this machine does have 8gb ram.