Here's how it happened:
I was at a friends house. He was out for a while, so I was playing a ame on his laptop, an MMORPG called Grand Chase. His laptop has no sound, so I decided to use my laptop for some music. For some reason, my internet connection was terrible, and this game requires a good connection, which is why I was using his to play.
Anyways, everything was running fine on my laptop. iTunes was running like it should, my music was playing flawlessly. Then, suddenly, without my doing anything, it started to glitch and lag, almost like a CD skipping but ten times worse. I grew confused, and shut down iTunes and restarted it, but the same problem occurred. So I did my full maintenance - a virus scan [using Avast! AntiVirus Home Edition], a Spyware and Adware scan [using Spybot - Search and Destroy and Ad-Aware Anniversary Edition, respectively], did a disk defragmentation, and finally ran a full clean using CCleaner to fix registry errors and delete my temporary internet files. All in all, this all removed a wide array of problems.
Afterwards, my overall performance improved. I got my internet speed back for the most part, and most programs run normally again. However, my audio and video are still glitching, in quite a strange manner.
Any video I watch on youtube seems to glitch for about a minute in, depending on the length of the video, but then runs perfectly normally. However, if I try watching the same video on another site, like Myspace, it glitches and lag repeatedly throughout the entire video. My audio still lags as I described before.
Along with all the maintenance, I've tried deleting files, music, and programs I don't need or want, and I've tried doing a System Restore to a checkpoint before all of this started, but it won't let me. I get a message saying it was unable to perform the restore and it can't make changes to my computer. I've also deleted my game, Grand Chase, wondering if that's what was wrong, but uninstalling it did no good, and reinstalling it did no harm. So that can't be my problem.
My laptop has gone through no physical harm whatsoever, but is prone to overheating - however, i keep a clean fan on it at all times when it is in use. And since I don't know how hot is too hot for my laptop, if for whatever reason I can't keep it cool [lack of a fan, etc.], then once it gets warm, I turn it off or put it in hibernation until it's cooled down all the way.
I'm not extremely knowledgable with computers, but I believe I've done all the basic maintenance and cleanings, and my computer is still running horribly. So I'm sorry about a lot of rambling.. I wanted to help you all out as much as possible by stating what exactly is wrong, and what I've done so far.
Any help is HUGELY appreciated! I just want my computer back..