I suspect the malware might slow down my system or there would be several things to consider:
ie
1) Defrag your disk drives
2) Make sure you have installed the latest drivers for your PC. Generic drivers from windows might not show the responsiveness you get when installing the latest.
3) Use lighter programs (Norton just eats up a lot of resources therefore slowing down your PC. Try AVG or NOD32 AV programs)
4) Uninstall unnecessary software
5) Unclutter your registry by using programs such as CCleaner(as already suggested)
