How do I get my DPI back to 96 when it is stuck on 120?

I am running Windows Vista. I've tried switching it back to 96 and rebooting it but nothing changes.How do I get my DPI back to 96 when it is stuck on 120?
if you went through the proper steps ';Right click desktop/Personalize/Adjust font size DPI settings'; and it still has not worked try again.



And if it still wont take, go into ';Custom DPI'; and set it too 100% but make sure too have the ';Use windows XP style DPI scaling'; is Unchecked.