A few days ago my computer has been stuttering. I'll have iTunes open listening to music while browsing with Firefox and maybe I'll have AIM open. Definitely not intense computing. And then every once in a while (either randomly or semi-randomly when I click something) the audio will crackle and the mouse will lag. It lasts like .1 of a second but it is very annoying and I've never had this problem until recently. Also my computer has locked up a couple times in the last few days. The computer just stops and everything is frozen including the mouse. Ctrl+alt+del doesn't work, only a manual restart on the computer does. My suspicion is a dying HD (http://www.newegg.com/product/product.aspx?item=N82E168...) . I just got it early January.
This should not be happening on a system with a Q6600, 4 gigs of RAM, a 8800GT, and an X-fi Platinum. You guys are the experts, any opinions?
EDIT: OS is Vista Home Premium 64-bit. I'm currently scanning the computer head to toe with various malware programs.
First, most of the time the problem is happening due to some new changes applied on our system either it's SW or HW.
Try to remember what is the last thing you did to your computer before it started to happen. E.g you're adding memory, or installing software, or applying patch/update whatever ...
In case of installing software or applying update, just uninstall whatever it is and see if it's help.
In case of HW addition or changes, try to reset your BIOS first and see if it's help. Otherwise remove your new HW etc
Second, I have similar problem with my system (E6750, 2GB RAM, HD3870) and it turns out to be my LG DVD-RW. For some reason, if it's playing some DVD the system will freeze. Your case seems more random, but if you were playing music from DVD or CD, remove it to see.
Third one, it could be your HDD as you said. Try to do the surface scan if there's any bad sector.
Fourth, I'm suspecting your Vista 64bit since the 64bit are still not yet widely used and supported by other HW/SW vendors. It might be that some of your HW (esp. the drivers) are not 100% compatible with the 64bit version. I can not tell which one, but try to see all the documentation you might have.
Last one, if all fails then you should consider to re-install your OS from the scratch (I don't like to do it myself since it's really time consuming )