- How much RAM do you have?
- How much free space is on your hard drive?
- What other apps are open when your finder is doing this?
- Take a look in Activity Monitor, and see if there is some process going on that is using too much memory or CPU.
- Try some routine troubleshooting and maintenance maneuvers, like booting into your recovery partition and repairing your HD and permissions. When to Run First Aid in Mountain Lion's Disk Utility - For Dummies
- Try a test user account. Isolating an issue by using another user account
- Here is a general reference about the SBBOD: The Spinning Beach Ball of Death
Thanks for your fast reply!
I have 4GB RAM and more than 360GB free space. That shouldn't be the problem.
There are no programs open besindes the finder since every program needs 5 minutes alone to open and opening more than one causes everything to crash and freeze.
I checked the CPU activity, (sorry forgot to say) but nothing unusual. less then 10% with finder and one program running.
Disk Utily told me everything is fine.
I haven't tried to log in via a second user account, because I managed to update to 10.8.5 after ages of waiting and everythings seems to run as usual again.
I'd be interested, though, where the problem might have been.