Okay, It seems the basics didn't help much.
It is quite possible that your directory on your hard drive is corrupted and is causing this type of behavior.
The next thing I suggest is called a safe boot, it runs UNIX routines that sometimes get neglected.
To do a Safe Boot, restart and before the first chime press and hold the 'Shift' key.
Wait until you see the Apple logo and the spinning gear appear, then let go.
It can take as long as 20 minutes to load, so please be patient.
When the login screen appears it will say in red on the login window 'SafeBoot'.
Now login and give it a few more minutes to finish loading.
Try doing whatever it was it was giving you the problem. If it works then probably the problem is solved, so restart normally.
If the problem persists then restart normally also, other fixes will need to be done.
Try that, it may need more than this, but this is the next step.
Let me know the result please