I can't see anything in KSysGuard under the tab of graphics. I do see RAM usage, but no CPU or Net usage.

Using 4.6 vainilla on Arch.

there might be something amiss in you ksysguard files in that you should see cpu, ram and network graphs in the default "system load" tab, at least I do on my system. Try removing or renaming ~/[.kde|.kde4]/share/config/ksysguardrc and the directory ~/[.kde|.kde4]/share/config/ksysguard

or you can create a custom metrics tab(s) and populate it
file -> new tab
the new tab will have drop zones on the left and available metrics than can be dropped on the right

I tried removing the file, but the problem persists.

Also, I don't want to create a new tab with info, I want KSysGuard to start working again as before.

Any other ideas?

did you also remove the directory?
if you create a new account does that user have the same issue?

I didn't remove the dir because I have a lot of custom config inside it.
Creating a new user did worked, so I guess it's a config prob. What now? Maybe diff the files related to net and cpu activity?

I fixed it after playing a while with the files/folders created for the new account. The problem was inside kde4/share/apps/ksysguard.

One of the files was missing a few lines.

Thank you for the help!