You might delete only the NAV portion of System Works to see if in fact it is slowing down your PC. You can reinstall it but then need to go through the "Live Updates" to get current.
I have used Norton Systems Works since 1999, Versions 2000, 2001, 2002, and 2003 in 3 computers with only one tiny hitch just a couple months ago on Live Update. It was resolved with no problem by just clicking on posted info at Symantec. I have the 2004 version, just waiting for subscription to run out before installing.
CNet is currently having "slow down" problems with the Community forums including this one for the past several weeks. They are still working on it.