Screensaver/Sleep problem

[AntV]

After updating my iMac to snow leopard it doesn't start the screensaver or "sleeps" after the set amount of time (neither display nor computer sleep).

I tried activating them via the hot corners and they do work, so I suppose there should be a problem with the timer or something, but I don't know how to check or try to fix that.

Any ideas of what I could try/do to fix this?

EDIT: Apparently there are more users with this problem... After about an hour googling I found this:

To fix the issues with the screensaver not working properly, go to your home folder, then go to Library-Preferences-ByHost and delete the following plist file:
com.apple.screensaver.*.plist
*Note: Instead of seeing the star as above, you will see a bunch of numbers and letters formatted like this:
xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
this is an ID number specific to your account on your Mac.
Now log out of the current account, then log back in and open System Preferences. Go to Desktop & Screensaver, and choose the Screensaver tab. Now set your preferred screensaver and settings. The Screensaver should now work.

And this:

To fix issues regarding Display Sleep not working properly, go to your root folder (called "Macintosh HD" by default, and then go to Library-Preferences-SystemConfiguration. Delete the following plist file:
com.apple.PowerManagement.plist
Now log out of the current account, then log back in and open System Preferences. Go to Energy Saver. Now set your preferred settings. The Display Sleep should now work.

I did both and nothing happened