Some Tips for SP installation
1.If you are on the medium or big farm, after doing a patch update/hotfix, run the config wizard in all the servers and come back to the application server and run the config wizard, else you might encounter a concurrency error. 2. If you are trying to replace the content DB, DON't attach the new one before removing the existing one. Else, you might get some weird behavior after the restore. Also, make sure that you go and change the site collection administrator for the site you replaced the content DB.