why does my pc run so slowly?

[simpsonD]

Everything was working fine, and then one day the PC started to run verrrrrrry slowly.  I thought it was a virus or spyware, so I downloaded new versions of anti-virus and anti-spyware from McAfee.  The problem is still there and the hard disk is constantly being accessed without me doing anything.  Any ideas??

 

[NetSquirrel]

I don't know much about this kind of thing, but my initial suggestion would be to try a defragment (Start > Programs > Accessories > System Tools). This is meant to rearrange the data on the hard drive into a more logical order, or something, so it should not have to work as hard. If it won't let you do that, this could mean that data are being constantly written to your hard drive for some reason (Disc Defragmenter stops if you change the contents of C:\). Some virus or similar program might cause that but I wouldn't know. The only other thing I can think of would be if there is an extreme shortage of available RAM, and the hard drive is being used instead (Control Panel > System > Advanced > Performance [Settings] > Advanced > Virtual Memory [Change]). I recommend setting this to "System managed size" as this seems to work without any problems. If you know where your RAM slots are inside your computer, you could check to see if one of the cards has come loose, or try relocating a card to a different slot. But don't try any of the above until someone answers who knows what they're talking about!

[dodgyshirt]

You probably have something running in the background which is hogging the PCs resources, have you installed anything new recently? Windows Task Manager/Processes should reveal the culprit.