Try dragging the finder pref file to the trash (don't empty the trash right away), restart and see if this works.
Path to file is this:
Macintosh HD ->
Users ->
Your Home Directory ->
Library ->
Preferences ->
com.apple.finder.plist
If that doesn't work, download
MainMenu and clean out all the user caches, deep clean the system, clean font cache. Restart. After emptying the caches, the restart will be longer than usual so don't worry if you notice it is taking a while longer to reboot.
If that doesn't work, create a new user account, log into that new one and use it, see if the problems persist in the new user account.
If not then it means that your usual user account has corrupted data in it. If the problem reproduces in the new account as well, then this means the problem is system-wide.
Report back with your results to these various troubleshooting ideas.