Acer :: Immense Speed Decrease In My 8530G Notebook

I bought my Acer 8530G Notebook a few months ago for the start of university. I picked it so that it could function as a desktop, whilst being able to tackle new games reasonably well. At first, it was fantastic, running games on high quality with lag only rarely. But then it began to lag immensely after about one month of me owning it. Not just in the games, but on the desktop aswell and when surfing the net. Also, sound began to crackle when I played music. It only cracked a little when using the built in speakers, however when I used earphones, the crackling rendered music unlistenable.

I began to think about what may have caused the problem. I uninstalled some of the larger programs on my computer to free up hard drive space, then got rid of additional applications that ran in the background (None that came pre-installed, mind, although they were few), then did full virus scans to check for anything malignant. The scans came up clean. all clear.

Even after all this, the performance is still -poor.

So I was wondering if any of you people have suggestions on what may have happened, or if the Acer 8530G has underlying problems?