Mouse won’t click and drag

i have a mid 2011 iMac. 2.7ghz i5. 12gb 1333 mhz ddr3. I am running the latest OS and I may have caused this issue myself as I am not strong in knowledge and I was fiddling about with my system user name which seems to to have caused this. The Machine works fine in all respects except for the click and drag which I was trying to use to delete a couple desktop files. Finder keeps freezing up and I have to force quit. I have tried reboots and restorations and reinstalled the OS and nothing works. I have tried various fixes from this site from users with similar issues with the mouse and or finder and nothing works. I was able to fix the user name issue but need help with drag and drop and freezing up of the finder app. The next stage will involve spending money so I am looking forward to trying out a few suggestions first. Thank. You to anyone that can help.