It can help if you can explain with a little more detail - more than "apps don't work properly"...
Do you have the same problem with ALL apps?
Does that same problem happen EVERY time? That is, always the same error, or the same app that crashes, etc ?
Does nothing happen when you try to launch an app (nothing happens, and you don't see any result when you double-click on an app)?
Or, the app launches, but immediately quits (and you see a window telling you that the app unexpectedly quit, or some other error message)?
Or, the app launches, and looks like it is working, yet you can't get anything about the app to function?
Or, your Mac just freezes (no mouse movement, etc)
Finally - it sounds like you can - sometimes - get everything working. What trick do you need to get everything to work, at least for a short time? (Shut down completely, or do a normal restart, start up first in safe boot, then restart normally?)
Is this still your 2010 MBPro, that has multiple problems?
Exactly how much RAM is installed?
Try reseating your RAM.
Another idea to think about - your hard drive may be on the edge of failure.