How to speed up a computer?

you're confusing trojans and viruses. And a decent, up to date AV will find both.

Replying to #21

But it's possible that his pc is infected (zombie).

If you can play your minecraft offline, try that and look that the results

Loony. I have around less than 1gb hdd drive space and it works a dream.

Replying to #24

3 weeks ago I had to fix a laptop that wasn't shutting down, it had less than 5GB free disk space. I emptied the recycle bin (had 16GB of stuff in it) and it worked fine afterwards.

I hope they didn't pay you for that :). What is the data disk thing do ?