Memory Problem?

Sorry for the life-story here guys and gals, just want to furnish you with the info/symptoms you need in order to make a diagnosis...

Recently rcovered from a bad infection (the computer, not me) of some sort or other... virus I think. To cut a long story only slightly shorther, after a pal messed around with the registry and dos etc and didn't get anywhere, we used the rcovery console.... 15 minutes later I was up and running again. More or less back to factory settings, everything seemed fine. However, when I come to open a folder or memory card of jpegs with a preview (thumbnail or filmstrip) it's taking several minutes to generate the previews for say 20 images, and seems to be struggling at that, if you know what I mean. It used to take moments to open the folder and generate the previes for a full folde/card of hundreds of images. Sometimes now it doesn't even mange to do it, and I get messages referring to 'pageing file' ?

Also, when working in Photoshop, a similar thing is happening... struggling to open more than a handful of images at once. It used to open a dozen or more large files smoothly and in seconds. Now, when I've been editing images for a few minutes, I get error messages referring to the 'scratch volume'.

Help!

Edit - Compaq Presario