It is possible that you may have a corrupt settings file.
Here are the instructions from PokerStars
https://www.pokerstars.com/help/articles/reinstall-instructions-win/7848/
Note that these instructions say to save the settings file (user.ini) and the notes file.
Follow the instructions in the link, but do notreplace your user.ini file.
If after the re-installation, the problem is solved, close the client, and replace the new user.ini with the one you saved.
If the problem comes back, you know where the problem is.
You can then re-install again, then go through all your settings using the client, and change them all to the way you want them.
I would suggest though that you wait a day or so.
PokerStars had stability problems over the weekend, and had to cancel several tournaments, and the problems you are having may be related to that.
I am experience no lag, and my auto-rebuy works and I'm able to open several tables -- all of these problems have been reported recently.
Now if I could only get 888 to work!
VS